Passengers have been offering advice on how to get a free upgrade on flights / Rex Features

No 1: be polite

The excitement of flying somewhere new is often overshadowed by fears of a busy flight with limited leg room.

But users of question-and-answer wesbite Quora have shared their tips on the best ways to get a free flight upgrade.

One user advises others to get intentionally “overbooked” and to “intentionally travel on holidays and other high-volume times” because this tactic sometimes results in airlines having to bump you up a flight class.

Another user says travelling on a Saturday - popular with families but less so with lone passengers - results in a greater chance of receiving an upgrade.

Glyn Williams said checking-in late and dressing smart have proved successful.

"Airlines routinely sell more economy tickets than they have seats. Sometimes the economy cabin is overfull... If you arrive early, you are not going to be reassigned. You'll be assigned the economy seat you paid for - no matter how sweetly you ask," he said.

But for many, being polite to the check-in staff iskey.

Jon White says: “I have found a hack that I have had some success with.”

“Firstly, be extremely polite and chatty to the desk staff… Laugh and joke with them – they will probably appreciate a nice customer for once. [Then, ask] if there are any upgrades available for purchase."