Ok - quick google and this is what Durham's archaeology dept : has to say In the event that you wish to change your degree course, you must present yourself to the departments concerned within the first four weeks of the academic year, or at the time of registration for the next academic year in June. No transfers will be allowed after this time. You would be ill-advised to change course outside this time anyway because of the amount of work you will have missed.
To ensure the quality of student experience, we have target quota for each of our degree courses and winning a place on these degree courses is very competitive. It is possible to change degree programmes, but there is no automatic right to do so. The factors we take in to account are academic merit as well as availability of places on particular programmes. If you wish to change one or more modules, or even the degree programme you are studying you must seek advice from the department(s) concerned at the earliest opportunity. In Archaeology, this must be from the Director of Undergraduate Studies.
You will normally need to satisfy any pre-requisites for the module(s) or programme to which you wish to change. If you are permitted to change module or programme it is your responsibility to catch up the work which you have missed.
Transfers will not be supported, except where students have met the standard offer, as if they had applied through UCAS for that course, or other appropriate standards of entry for the course. However, meeting the standard requirements for the course is not sufficient alone for entry to the course. The acceptance of a student for a particular programme or set of modules will depend on the availability of places in the receiving programme as well as the ease, complexity and equity of the proposed arrangements, and cannot be guaranteed.
Students wishing to transfer into, or out of, Archaeology programmes must follow guidance and directions given by the Director of Undergraduate Studies who is the sole contact for any discussions about changing degree programme. You will also need to contact the appropriate advisor in the ?receiving? department. If both departments are in agreement, you will need to obtain a form from the Student Planning and Assessment office and written approval from both Departments. Acceptance of your transfer must be proposed by the Director of Undergraduate Studies and approved by the Board of Studies, subject to Faculty approval. If, in exceptional circumstances, you wish to transfer after the first four weeks of the academic year in addition to agreement from both Departments, as above, you will need to seek a concession from the Dean.
I'll see if there are similar things on tyhe geology etc pages.