Right up until Margaret Thatcher’s time, the UK had currency exchange restrictions for private citizens (as did many other countries - the exchange rate wasn’t floating but managed). There were no restrictions on travel, but there were restrictions on how much money you could take out of the country or change into foreign currency before leaving. When you bought foreign currency or travelers’ checks at the bank, they would register it in the back of your passport (which you had to produce). Of course, you could just stuff cash down your underpants and go, but above a certain amount that was illegal.
Back in the 40s/50s the amount was pretty restrictive. Unless they had an offshore source of funds, most British people couldn’t take lengthy personal trips abroad. That said, they couldn’t have afforded it anyway in the days before cheap air travel etc. By the 60s/70s the limits were eased.