Taking courses in addition to your normal course load is known as ‘Auditing’ and is not encouraged at UCL, as you are expected to put all of your efforts into the courses for which you gain credit and which contribute to the completion and classification of your degree.
In rare cases, lecturers will allow you to audit their course if there is space available and if you have permission from your Personal Tutor to attend, e.g. the course will make a useful contribution to your other credit-bearing courses. However, some departments, e.g. the Centre for Languages and International Education (CLIE), do not allow auditing for any of their courses.
If you are permitted to audit a course, you would normally only be able to attend the lectures, as seminar attendance is rarely permitted. You would not have to submit any assessments for the module and it will not appear in your personal timetable or on your final UCL transcript as you would not be officially enrolled for the module.