you don't need to be a resident of the UK to open bank accounts there.
what one branch may tell you in regards to these rules will change from branch to branch. just because one customer service agent︀ says something doesn't make it fact. most staff make things up as they go, if︁ they don't know the answer.
to open a bank account in the UK you need︂ Proof of address. just go to your local bank wherever you are, and get your︃ address changed to your UK address, then get them to print a physical statement and︄ stamp it.
alternatively, open a bank account with HSBC wherever you are, and get them︅ to open you an account in the UK branch.
if you want a credit card,︆ and have an amex, amex will open you a UK amex via global transfers. You︇ already need a bank account in the UK though.
If you have a visa for︈ the UK, can open an account not physically present through Ifast global (still need that︉ proof of address)