But ther will be record of you taking from a savings account, or selling investments and HMRC may well ask where that money went, if there is no evidence that you spent it on yourselfs.
Remember every financial institute has to file a complete financial statement with the HMRC every year listing details of all customers, interest earned etc, so theywould quickly pick up any unusual movements of money.
On the other hand, if the money is excess income and it is clear it comes from your monthly income after all your normal bills are paid that is OK.
I have yet to come across any scheme to try to cheat the revenue, thought up by what I would describe as the man or woman on the Clapham Omnibus, that hasn't been already noted by HMRC and made impossible or illegal, with good traps for catching the gullible and naive.
So, Nanawind*, find out what you can do, annual allowances, gifts on weddings etc, money invested for children, but do not try to hoodwink HMRC, they are far cleverer than you give them credit for.