I have a branch in London, and a couple of employees running it. I'm thinking of opening another branch in York. The thing is, I don't know how much I'll be travelling up and down to York, and may have to suddenly go up there at short notice if a customer calls. Would buying a season ticket to York be tax-deductible in those circumstances? I'm thinking of keeping my house in London, and renting a house in York. Family will probably be up in York. Would the Revenue claim that it's commuting costs?
The fact that you're renting a house in York and your family are living there tends to point towards you having two homes, so travel between wouldn't be allowable. Would be completely different if you and your family stayed living in London and you just travelled to York when business required you to do so. Your rent and housing costs in York almost certainly won't be tax allowable either if your family is living in it. Could be that York becomes your "permanent" workplace and then London would become a temporary workplace, thus allowing the travel costs, but not easy to get HMRC to accept if you still keep your previous family home in London and continue to live in it.
One thing maybe to look into would be whether you could claim tax relief on relocation - i.e. if your family move to York is permanent. Then you could claim rent on York for a short time until your buy something, and could claim removal costs, travel between for a short period, and relief for legal costs and stamp duty on selling London and buying in York.
Ultimately, the longer the time period where you're "living" into two homes, the more difficult it will become to get tax relief on travel between them. Remember the whole ethos of allowable expenses is that they have to be "wholly and exclusively". You breach that if you travel up to York on Friday for business meetings, but then stay there for the weekend for family reasons!