not so.
The taxman runs three standard tests on you, one of which is the cash test. You fail it when you spend more than you earn.
For instance you earn £25,000 in the year. £8,000 is in cash and you draw hardly anything from the bank because the mortgage and poll tax swallows most of it. Your petrol and other items you have reciepts for comes to £3,500, so there is a remaining £4,500 in cash.
However you have already told the taxman that you spend £60 every week at sainsburys, pay your utility bills in cash, and buy clothes for your children, yourself and your wife on a regular basis.You agree with the tax man that you spend £12,000 in cash every year. He can't understand how you can spend £12,000 when you only have £4,500.
You can say you borrowed it off a friend, or that you won it gambling, but the best way is to keep a cash record with a cash in hand figure.
Even if you were declaring £50,000, but only had £8,000 in cash the figures would be very similar.It is far easier to do this week by week than to try to reconstuct from scratch at the end of the year.