Re: The folly of individuals notwithstanding...
You must have some pretty crazy laws over there in the UK. I've never had problems withdrawing sums far larger than that in cash from my bank. They need to file a form with the government if you withdraw more than $10,000 in cash I believe, but they (at least the credit union I bank at) doesn't stop you from taking it.
I'd switch banks if I was ever denied being able to withdraw such a paltry sum!