There was a discussion about this a few months back: What if i need a **lot* of cash?
The recent government Taylor Review (July 2017) suggested that there should be a ban on paying cash-in-hand to tradesman such as a builder or window cleaner, etc. Whilst it isn’t law, the government is certainly going down that avenue.
In the end, if you need £1,000+ of cash then I would go into a more “secure” high street branch with my second account (it is always recommended have more than one current account in case access to your money is blocked or the account closed) and withdraw the money.