I may be starting to work remotely soon from the UK for a US company. From what I understand, holiday requirements are very different there (in the UK there is a minimum of 28 days PTO including bank holidays, but it seems in the US there is no minimum) so I'm not sure whether I could still expect the same time off as I'd get from a UK company, even if I'm still living here. Any advice?
These are questions to ask before you accept any offer. Send them to the hiring manager, hr person, or internal recruiter that you dealt with during the interview/etc process.
The good news is that, as was already pointed out in the comments, if you're working the in UK they're legally required to give you whatever the statutory minimum benefits are, do the employer side of UK taxes for you, etc. So unless the company is incredibly stupid (and you're their first overseas hire) that all should be covered.
In addition to verifying the number of days off you're getting, I'd also ask about expectations and (assuming multiple existing non-US employees already) typical practices when national holiday schedules don't match. Your taking a bank holiday when the US part of the company is working shouldn't be any more of an issue than your taking a random other day off. The real question is if they're expecting you to work solo on US only holidays (ex Independence Day and Thanksgiving) or take them off too; and if so if they're giving you extra days of PTO to cover that or not.