Types of tent
What you need is best described as a lightweight mountain tent. This is not to say that you will necessarily be camping in the mountains, but this is the type which is likely to serve you best. They are small and light, and designed to withstand wind and rain. They have an aerodynamic shape, so that the wind flows easily around them. They have a fully waterproof outer tent which comes right down close to the ground on all sides, and a separate inner tent made of non-waterproof fabric. Even in lowland Britain, anything less really won't do. To be reasonably comfortable, one person will need a "two-man" tent. Some tents are described as "one-squeeze two" size but, whilst they are lighter and more compact, they are really quite tight for one and two people would have to be very good friends indeed. The balance you need to strike is between comfort for a long stay and compactness/lightness for carrying the tent on your travels. The ultimate in lightness is a bivi bag. These are quite literally a bag made of breathable waterproof fabric, that is just large enough for you to sleep in. You really can fit them in your pocket, but for a stay of over a week, you might find them a bit impractical unless the weather was good enough for you to be able to do most of your living outside.
You will therefore probably want a proper tent with poles. Tents of this kind come in two forms: the traditional ridge tent and the more recent innovation, dome or tunnel tents.
Ridge tents A basic ridge tent is shaped like a pitched roof. At each end the tent is supported either by single upright poles or by a pair of poles arranged like a letter "A". The ridge may be unsupported, or held up by a ridge pole. The strongest ridge tents have both A poles and ridge pole, although this inevitably adds weight. The advantage of a ridge tent is that it uses the least possible amount of fabric and minimum mass of metal in its poles to cover a given floor area. All the very lightest tents are still ridge tents. Usually they taper towards the foot end - you don't need so much space for feet as you do for shoulders - again saving on fabric and poles. Tents like this have one short upright pole at the foot end and A poles at the head end, with no ridge pole. In the very best tents, the A poles fit into sleeves sewn into the outer tent, making them more stable. So far as I know all ridge tents pitch outer first; that is, you can put the inner tent up in the dry. The cost of weight saving in a ridge tent is the relatively cramped conditions inside most two-man versions.
You don't see many ridge tents in catalogues nowadays. Robert Saunders make some of the lightest and most compact tents you can buy and, if I were thinking of doing a lot of travelling I would go for their lightest model, the Jetpacker. It has been around for many years, but you can take it with you easily and it seems to be able to stand up to some pretty foul conditions.
Dome and tunnel tents Most modern small tents use a different arrangement. Flexible poles which slide into tunnels sewn to the tent fabric make a framework which supports the fabric closely. The poles are made either of glass reinforced plastic (GRP) rods, or of light precurved aluminium tubing (the aluminium is lighter and easier to repair). Many variants of this idea have now been produced. The basic design is the tunnel tent, with flexible poles arranged like upside-down "U"s at intervals. A small two-man tunnel tent might have two of these poles, but larger tents might have three or even five. The other extreme is a dome tent, either with three poles, again each like an upside-down "U", crossing at the apex, or with four or five poles arranged in a geodesic structure that is about as strong as a small tent can be. There are also many variants on these two themes, or combinations of them.
One advantage of a dome or tunnel tent is the increased space that they have inside. Another advantage is stability in side winds. The dome tents in particular can be pitched in any orientation relative to the wind direction. The major disadvantage is their somewhat greater weight and packed bulk - they have more total weight of poles and more fabric than ridge tents. Another difficulty is that the fit of the poles and the inner tent are critical, so quality really counts and a cheap dome tent can be difficult to put up successfully.
Quality and practicality
It is very hard to judge the quality of any tent without first seeing it pitched. Shops usually have some tents put up in their showroom, but you really want to see them outside. Some shops have a field or large warehouse area in which you can see a lot of tents. Mail order stores tend to be slightly cheaper, but there you have no chance of seeing the tents at all.
One indicator of the quality of a tent is the sewing. In a good tent, the pieces of fabric in the outer tent should be joined with run and fell seams. In these, the edges of both pieces of fabric are folded over one another into a sandwich arrangement, with two parallel lines of stitches running down the seam. A good run and fell seam is extremely difficult to produce, but is the strongest type of construction. If the lines of stitches are not straight, not parallel to the edge of the folded fabric, or repeatedly stray over this edge, then the seam is not well made and you should look closely at the rest of the tent. Run and fell seams should also be used in the groundsheet which is sewn into the walls of the inner tent, but the inner tent walls themselves often have a simpler and cheaper type of seam. In good quality tents using PU coated waterproof fabric in the outer tent the seams are all factory sealed by hot-melt tape. On the other hand, ultra-lightweight silicone coated fabrics cannot be sealed in this way, so the absence of factory sealing is not in any way an indication of low quality. The quality of the fabrics themselves is more difficult to assess. Very lightweight fabrics tend in any case to be rather flimsy and to pull a bit at the seams. A better indicator of quality is the poles. Do they fit together snugly and are their different parts joined together solidly? Generally speaking, if trouble has been taken over stitching, seam sealing and poles then the design is also likely to be good. Also, generally speaking, you pay for what you get and a cheap tent is likely to be of poorer quality than a more expensive one. You will need to balance the cost against the extent to which you think you will use the tent, but in the middle of a long night in a leaking, impossible-to-pitch-correctly, over-cost-cut tent you will certainly wish you had been able to find the extra. If you really can't afford a reasonable tent, then it is better to try to borrow or share one, or to sleep in the hostel which is available, at least, on the Institute's field courses.
You will also need to look at the features of the tent. The tent should be in two parts, an outer skin and an inner tent. The groundsheet (which must be made of fully waterproof fabric) should be sewn into the walls of the inner tent and made like a shallow tray, with its edges turned up all round at least an inch or so. If the field floods during the night, this means that there is less chance of it pouring above the groundsheet and through the non-proofed inner tent wall fabric. There should be some kind of insect-proof ventilation in the inner tent. The best tents now have a separate mosquito net inner door which can be zipped all round. Insects can cause real misery when camping, so it is well worth taking quite elaborate steps to exclude them. During warm summer nights in Mediterranean countries, you might wonder why you bother with a tent. The answer is, the mosquitoes, so make sure you can get good, insect-proof ventilation right from the start. For use in a wet country like Britain, you will also need a covered "porch" or "bell end" over the entrance to the inner tent. This is usually provided by an extension of the outer tent which gives enough space to manoeuvre out of the inner tent and into waterproofs before venturing out into the elements. You can also keep your boots there. The outer tent should come right down close to the ground all round, including the extension over the porch. These days, it is usually pegged to the ground through little knotted loops of elastic cord, covered with a braided nylon fabric (shockcord). If your tent is one of the old fashioned type, with what look like large rubber bands in the pegging points, these can be easily replaced with the rather tougher shockcord when they perish.
Using a tent
Fully waterproof nylon is used for the outer tent in most lightweight models of the kind that you will need. It has many advantages including rot-proof qualities and light weight, but it has the big disadvantage of being prone to condensation. It is not possible to use breathable waterproof fabrics for an ordinary tent because they work well only when wrapped quite closely round the body as in a waterproof jacket or a bivi bag. This means that you just have to minimise the condensation as much as possible, by ventilation. Most lightweight mountain tents have an inner tent made of a non-proofed fabric that allows the water vapour generated by you during the night to pass through. This vapour will condense on the inside of the fully waterproof outer tent which, during the night is much colder than the air inside the tent. Some of this condensed water will form into droplets that fall back onto the inner tent and in a good quality model, the inner tent fabric has been treated so that these droplets run off easily rather than soaking through. You will have to make sure, however, that the inner tent does not touch the outer tent, because the condensed water will then definitely come through. This is a problem particularly with badly designed dome tents and with too many people in a tent but, once you get used to keeping everything (including yourself) away from the tent walls, the problem is minimised. It's certainly worth keeping your spare clothes in a plastic bag, just in case they get pushed against the side. It's also well worth keeping your sleeping bag inside a plastic bag during the day. You can actually buy people sized bags made of tough plastic that you get into in case of total disaster (disintegrating tent etc.) - you would need to keep the mouth of this well open to maintain ventilation. Although in a proper mountain tent the outer walls come down close to the ground all round, there is an all important gap at the bottom. This is supposed to maintain adequate ventilation and avoid too much condensation. Usually it works quite well, but when you are camping in long grass the gap is covered up. The only way round this is to keep the zips of the outer tent part way open, even on a rainy night. This is one of the main reasons for having a good "porch" which prevents the rain from blowing onto you in the inner tent. Tents which has been designed for pitching in snow, where there can be no gap and the bottom, usually have efficient ventilators.
Do try out the tent before you actually go camping for real. Make sure that all the bits are there. Make sure all the seams are properly sewn. Take it back to the shop if anything looks wrong - and don't accept any nonsense from them - you are going to be depending on the tent. When selecting a site to pitch the tent, you really want quite level ground. If there is a slope, then make sure the head end of your tent is at the top of it. Sleeping with your head lower than your feet feels very strange and your nose/sinuses get congested. If you try to sleep across a slope, you will roll against the side of the tent during the night and possibly get wet. If you are one of two in a tent pitched like that, make sure you are on the higher side! The other consideration is the weather. With a good dome tent, this doesn't matter much but with a ridge tent, you need to pitch it so that the wind is not blowing across the long axis of the tent (i.e. not straight into the side panels which will then press against the inner). In aerodynamic terms, it usually doesn't matter much whether the foot end or the head end faces the wind, but you will ideally want the entrance to open away from it so rain doesn't blow in.
Finally, and most important of all, never allow a flame anywhere near a tent. Don't cook in the tent or anywhere near it. On most excavations, there are proper arrangements for cooking elsewhere anyway. Don't use a gas, paraffin or petrol lantern near a tent or, worse still, a candle. Don't smoke in or near any tent. Gales, rain and damp clothes are survivable, but a fire may not be. I know of people who have been badly burned in this situation.