Millions of people are still missing out on free flights from the airlines. If you’re one of them, now’s a good time to take advantage of one of the frequent-flyer or frequent-buyer schemes. They take seconds to join and can save you a packet.

They’re not just for jet-setters and business travellers, either. Even if you don’t fly much, join the right one and you can earn points by shopping at your local supermarket, filling up at the petrol station and paying your utility bills.

There are some juicy enticements. Airmiles, for example, is currently offering a 1,500-mile bonus for members who apply for, and spend £10 on, an affiliated Airmiles TSB credit card – that’s enough for a free return flight on British Airways to Rome, Nice or Prague (or two returns to Paris, Amsterdam or Brussels).

BMI’s Diamond Club is offering 4,500 points to anyone who joins up and makes a return flight with the airline before the end of November. That’s enough for a free one-way ticket to any of its European destinations.

If you’re worried that the airline you collect with might not last out the current crisis, it would be wise to dust off your log-in code and get booking. Any unredeemed points will be worthless if your carrier goes bankrupt, but you can use them to book a freebie with a stronger partner airline up to 12 months before you travel.

Whether you have points aplenty or haven’t yet taken the plunge, here’s how to make the most of the schemes.

How do I join? It can be done over the phone or online – contact details for the biggest schemes are listed below. You can sign up for frequent-flyer clubs at airports, too. Apart from the points themselves, it’s a good way to keep in touch with an airline, as it will e-mail you with deals and promos.

Which type of scheme should I go for? If you fly a lot on business, then an airline scheme is best; if you rarely fly at all, join the scheme that is affiliated to your local supermarket or petrol station. Airmiles, for example, has teamed up with Tesco and Shell, while Nectar works with Sains-bury’s and BP.

Both Airmiles and Nectar have improved, too: now, a free flight really is free, with the airline taxes and fees included; and the points no longer have an expiry date.

If you fly with a variety of carriers, there are three main airline alliances, each with dozens of members with which to earn and spend your points. British Airways is in Oneworld (www.oneworld.com), along with Cathay Pacific and American Airlines. BMI is in the Star Alliance (www.staralliance.com), which includes Air New Zealand and Thai Airways. Virgin Atlantic has 15 partner airlines, including Singapore Airlines and South African Airways. The last of the three big alliances is SkyTeam (www.skyteam.com), with Air France/KLM, Continental, Kenya Airways and others.

How can I get the most points? You get points every time you fly with an affiliated airline or shop in scheme-member outlets. Airmiles members, for example, earn points from John Lewis, Homebase, Waterstone’s and eBay. If you pay with a club-affiliated credit card, you’ll typically receive a point for every £1 you spend. Use the card at a member outlet and you’ll get twice as many points on a single transaction.

What’s the best way to spend my points? Many schemes have zones for spending. For example, Airmiles Zone 1 includes Paris, Brussels and Amsterdam, while Zone 7 covers locations such as Sydney, Perth and Buenos Aires. It’s best not to waste your miles on the shorter flights, as these are cheap anyway, thanks to no-frills carriers. Instead, wait a little longer and cash them in for trips further afield, as you’ll save a lot more.

If you are within reach of the next zone, you can usually buy top-up points to get you there. Within a zone, choose wisely: under the American Airlines scheme, which is fairly typical, the 40,000 points needed for a return to New York will also buy a round-trip ticket to Hawaii or the Caribbean.

Your departure date also makes a difference. Under the American Airlines scheme, a return to the USA requires 40,000 points in off-peak periods; at certain peak times, the figure rises to 60,000; and to grab the last seat on a busy plane, you may need as many as 100,000.

Your points can also buy an upgrade or a flight for someone else; you can even donate them to charity.

Can I convert my points into cash? No. Nor can you sell them any more, though there was once a lively trade on eBay. In theory, you can use your points to buy flights for someone else in exchange for money, but you risk being thrown out of the scheme if you do so.

Contacts: Airmiles (0844 493 3399, www.airmiles.co.uk ), BA Executive Club (www.ba.com), BMI Diamond Club (www.flybmi. com), Buy and Fly (0871 282 4680, www.buyandfly.com), NatWest YourPoints (0845 072 7629, www.natwest.com/yourpoints), Nectar (0844 811 0811, www.nectar.com), Tesco (www.tesco.com) and Virgin Atlantic (www.virgin-atlantic.com ).