No of course not. The banks are guaranteed up to a certain amount per account holder by the Government, is it £50K? - much more than I've got in the bank, anyway. If everyone did that, there would be a run on the banks, then the whole system would be in trouble. Where would you keep it? It certainly wouldn't be insured if you were burgled or the house caught fire.
Not only are your funds safe in the bank, with the Government guarantees etc., you can earn some interest if it is in a savings account which would go some way to offset the loss due to inflation, which you wouldn't get if your money is tucked away under the mattress in cash!