https://www.financial-ombudsman.org.uk/businesses/complaints-deal/banking-and-payments/bank-account-closures
The Financial Ombudsman Service says they expect at least thirty days' notice if closure even if the notice period in the Terms and conditions us shorter. They say a reason need not be given but it helps if it is.
A complaint can be made to them and if they decide the notice was too short, they can order compensation for financial loss or distress.
If they decide the account has been closed for the wrong reasons, they can issue a Direction that it be re-opened.
It does also say banks should not close accounts "because of unfair bias or unlawful discrimination."
Having said all that, it's a big leap to suggest it was done, "at the behest of the Gov. or one of their agencies."