mumsneeds in a sense as we have been sleep walking into a police state we DO have occupational laws now. We cannot even leave the house in England at the moment expect for a very very limited number of reasons.
On the legal issue we don't know what laws will apply in December when students want to come home. If the university for those in its halls if you do not leave by X date then you will not be allowed home at all - I would start by looking at the terms and conditions relating to that accommodation which probably gives a student a right of occupancy/ a contract to stay in that place as much as they like up to July ( I am leaving Oxbridge out of this as they tend to have 8 week terms, obligation in most cases in normal times to stay within the area and not go home during term and they often let your rooms to others in holidays so all very different).
There is probably some general clause in the contract every student has with the university about following university rules, right to fine you if you drive a lorry over the university grass or set the place on fire or make far too much noise but those terms have to be fair and reasonable otherwise they will be invalid under the Consumer Rights Act 2015.
The bottom line is universities have a lot of power which is sometimes exercised unfairly as they can be the difference between your career or no career so people tend to follow the university line.
My 22 year old in Bristol (not at Bristol U but another institution - 100% on line) has had nothing by email or post about times for coming home and is in a private rented flat.
Like the stay 2 meters apart which I believe is not in the law but just a recommendation probably suggestions as to when students go home may just end up being voluntary with the ope that if most obey them then that will mean less infection although in my view if they come home staggered that probably means less infection so if the plan fails of the state then more lives may be saved.
Also some universities and their hired security staff seem to be going a bit far and beyond what the law says and need to be reined in. Eg some patrolling security guards are not aware that students might be a bubble of 15 and are telling a group of 15 in their own halls not to be together thetab.com/uk/bristol/2020/11/11/bristol-students-say-security-have-hit-them-and-burst-into-flats-in-explosive-leaked-report-42953