The one most effective way ordinary travellers can get a free flight upgrade

It is possible for ordinary travellers to get a free upgrade without air miles, especially if he or she has a flexible schedule, according to frequent flier and points expert Gilbert Ott, who runs the air miles site God Save the Points.

Ott has made a career out of helping fliers use miles to get free seats in business and first class. He even once bagged a free ride on a private jet.

"Upgrades are generally a function of loyalty and money spent," according to Ott, though he says there is one effective way to get an upgrade that does not require thousands of miles or elite status.

Use oversold flights and schedule changes in your favour

One "very good trick" to getting an upgrade "is to use oversold flights and schedule changes to your advantage," Ott told Business Insider.

"If the flight's oversold, [the airline will] usually ask for volunteers who are willing to take the next flight," he said. "I call that a 'bumpertunity.'"

Flexible travellers who are happy to take the next flight are more likely to get money back from the airline for the inconvenience, Ott explained, adding that many airlines will also let you fly up-front on the flight you're moved to.

Ott gives a hypothetical example of an oversold flight to Los Angeles, for which he has paid $300 (about £231). In return for switching to another flight, the airline might give him a $500 (£385) voucher for future travel and bump him up to business class if there's space.

"I'm getting more money than I actually paid for the ticket and quite often I'll also get the upgrade too," he said. "That's your best opportunity if you don't have miles or status with the airline."

Admittedly, for people who do have miles, getting an upgrade is easier. In that case, Ott recommends booking "flights that have instantly upgradeable space."

"If I'm booked on Virgin Atlantic economy and I want to upgrade to premium or business, I'd look before I book my flight to see if that flight has seats available in business or premium and if it does then I'd be able to upgrade instantly," he said. "I'd make the cash booking and then 20 seconds later I'd call, and boom, I'm upgraded."

As for old-fashioned methods of getting an upgrade, Ott says not to bother. "Wear the suit, put on the cast and pretend you've got a broken leg - that's not gonna happen."