I don't claim to have followed every last detail of all local lockdown regulations, but I have looked at some. What they have generally done is to make it a criminal offence for people living in the lockdown area to meet in each other's homes (including gardens) without a reasonable excuse. This also applies even if the person you are meeting lives outside the local lockdown area. Bizarrely, it has still generally been perfectly legal to go to the pub! To date I don't recall seeing anything in local lockdown regulations which would prevent someone going back to university. I don't think the regulations address the position of students who live at one address in term time and a different one during the holidays.