They’ve publicly stated what their customer numbers are. They’re above two million IIRC. (That’s unique customers, not accounts) and billions (10 I think) in deposits. The news was shared back in the Chase thread (I’m sure it was you who asked for the data too!).
Edit: remembered it wrong, but was close:
1 million customers and 10 billion in deposits (both are likely to be higher now if the trajectory they’re on has held. So 2 million will be close if they’re not already there. It wasn’t you who asked for it, but you did reply to a quote referencing the customer numbers.
Halifax have a noticeable branch presence here and advertise heavily on tele. It’s nice to see Monzo and starling do so well but there will be a large section who still want branch services. I think the northern Irish only banks fell behind a long way with their digital offerings so others picked it up. Halifax, Santander and nationwide are common, hsbc and Barclays don’t have many branches.