This relates to entry requirements to get onto A level courses – which will vary depending on the college/sixth form you want to go to.
I imagine that many will require a minimum in Maths and English language, perhaps a 5 (C equivalent), in order to progress - but again it will depend on where you are applying to or continuing on at. In terms of university, unfortunately a 4 in Maths GCSE wouldn’t be sufficient to meet UCL’s basic entry requirements.
All courses at UCL require GCSE passes in English Language and Maths at grade 5 or higher, and some courses may ask for higher grades in these subjects. You’ll need to check the website for exact requirements for the course you’re interested in.