HMRC view
Umm, as I understand things, if you mainly regularly work at a specific location for two or more years, then according to the UK's HMRC, that is your designated place of work for tax and expenses rules. This would mean that anyone who has been told to work from home for the last two years, and done so, would have no legal claim to work in an office building, even the one they used to use.
Now, that could mean being able to claim expenses from your employer for any trip into 'the office', but it could also mean that your employer might no longer be required to provide you with any office, and could then save the money of heating, or even having an office building.
I think we need a lawyer specialising in employment law to provide 'an opinion' on this one.*
*Well, those of you who are still employed might, I'm retired so watching from the sidelines, as it were.