Yes they can be, and in the case of 10 Downing Street, the garden is part of the office. Don't you remember that presentation for the media of Nick Clegg and David Cameron embarrassingly pretending to be friends in their new coalition, in the garden of number 10, their office:
They look as though they are having a party !
Is that a glass of gin I see?
The garden was in use as a work space on that occasion. On the day of the party, the garden was a party venue. It is possible for a space to be used for different activities. Just because it has been used for business previously does not mean it can never ever be used for any other type of activity, that’s preposterous.
Here is an example from my place of work (before retiring): The aircraft hangar was a place of work. It housed the aircraft, daily aircraft safety checks were carried out there, and minor engineering tasks were performed. In no way could it be deemed a party venue. It was used for work purposes almost 100% of the time.
A few years ago, a colleague retired and we held a leaving party for him in the hangar. Food, drink and music was laid on. We had been working from 08:00 to 18:00. The party started at 18:00 and from that moment onwards, the hangar was no longer a working environment. It was a party venue. Had covid restrictions been in place, we could not have held that party. It would have breached the rules and we would have definitely been sacked.
What I have described is exactly what happened in the Downing Street garden. The working day ended and a party / social gathering with drinks, music and behaviour which damaged property began. All in breach of the Prime Ministers own rules, which he had read out on national tv. The party also had his approval / blessing. He’s lied to parliament about it and he must resign or be removed from office.
It’s not a witch hunt, it’s holding people to account and making them responsible for their actions.