Odd. I called in at the Ipswich branch of Santander yesterday. The guy on the door asked me what my banking requirements were and I told him that I'd like to reactivate one account, that they were about to make dormant, by transferring the funds from an already dormant account into it (with the dormant account then being closed). He said that he could do that himself and scuttled off to find a colleague to cover his door duties for him. I was the shown into an office and everything was sorted out quickly and easily for me. (The branch was fully open to customers, with no references to access being limited to vulnerable people. Customers were being allowed inside to engage with counter staff or, to save them waiting in the queues outside, just to use the internal cash machines).
Your simplest solution though would be to book a telephone appointment with your branch. They're available in 45 minute slots and, based upon what I've just seen when I looked at the details for their Ipswich branch, there are loads of slots available tomorrow.
To book an appointment, start here:
https://booking.santander.co.uk/branch-appointment-booking/?stepNo=1