Hi,
I checked the situation with the access you provided.
And while I was able to "reproduce" the problem with an existing address, I wasn't able to reproduce the problem with a new address.
And checking your zones, I can see that you created a new "united kingdom" country zone and unpublished the previous one.
However, in your bank transfer shipping method you only have the new zone selected.
So if someone created an address with the old "united kingdom" zone selected, and if he tries to use that address during the checkout, it's normal that the payment method doesn't show up as it's configured to only display for the other "united kingdom" country zone.