I plan to visit London with my daughter in this August. I wonder how much pounds I should exchange from bank.

I'm used to cash and think credit card risky. So I never applied for a credit card before. Now I've to request one to book fligths and hotels. I decide to cancel the card once after I return. I want to use cash as more as possible. But I don't know if it is reasonable to do like this in London.

Your experience is appreciated.