Buying something on 'tick' is a British idiom that means to buy on credit.
It might be used alongside other idioms, like to buy on the “never-never”. Often people would use both.
Another way of paying later that was popular in pubs was to buy drinks and then ask the barman to "put it on the slate”.
It probably helped if you were friends with the publican.
In many ways it was a system based on trust.
Buying on “tick” and the “never-never” or “putting it on the slate" were all forms of credit, but not in a legal sense. Typically, it was often a private arrangement, and perhaps most importantly, there was usually no interest to pay. In other words, you just owed the shopkeeper or publican money for goods purchased. It was one way of helping customers through the week until they got paid. It worked as long as you settled your bill on time; otherwise, you might end up being banned or barred.
And it was different from purchasing items by using an actual credit card. The first credit card was introduced in Britain on 29 June 1966 by Barclays, but it would take a long time for their use to become widespread. For the most part even paying by cheque was rare. Most people didn’t have a chequebook or that type of bank account.
In fact, many people didn’t even have a bank account.
And debit cards were also some way off in the future as well.
The 1960s and 70s were a time when cash was king.

