£1M:
Wouldn’t change my life, but I’d stick it away in a brokerage account, where it could grow for later.
£10M:
Declare Monaco as my home.
Give each of my 3 siblings £1M
Give each of my kids £2M
Put the remaining £5M into a brokerage account and transfer the conservative 4-6% annual return (£200-300K) to an account that, when added to what we already have put away, would allow me to basically do whatever I wanted, whenever I wanted, forever. Some of those proceeds would be for charities, some for travel, some for philanthropic ventures (educational scholarships, habitat for humanity-type endeavors, etc...). Oh, and a Tesla roadster/Acura NSX/Porsche Taycan/BMW i8 style vehicle!
£50M:
See above, plus live off the £2-3M per year in dividends and interest, add a Citation X, and have a few pied a terre around and about (Hawaii, Lake District, NZ, Caribbean maybe), then become Lord Lucan Mark II!