You don't have to stump up a fortune to get the right lotion. Jill Papworth reports

Suntan lotion can cost as little as £2.50 a bottle through to £20 or more. Do you get what you pay for? We gathered advice from respected sources including the NHS, SunSmart - the national skin cancer prevention campaign run by Cancer Research UK cancerhelp.org.uk and online medical website netdoctor.co.uk to find out what really matters.

It's a myth that you need to burn in order to tan. Sunburn is painful, unattractive, ages your skin and increases your risk of skin cancer, so you should do everything you can to avoid it.

Dermatologists say you should choose a sunscreen ...

... With an SPF (sun protection factor) of 15 or above - this will give you more than 90% protection against harmful rays. SPF15 blocks 93.3% of UVB radiation, which causes sunburn, protecting your skin up to 15 times longer than if you wore no protection.

Be aware that SPF numbers on products outside Europe may be double those on European products eg, an American SPF 20 usually means the same as a European SPF 10. So check which system you're buying.

... Labelled as "broad spectrum" This will also protect you from harmful and ageing UVA rays (as well as UVB) which are now believed to increase the risk of skin cancer. There's no international measurement of UVA protection. The UK uses the "star system", ranging from zero to five stars, where the higher the number, the greater the protection. But this system only measures UVA protection in relation to UVB, so can be confusing. A sunscreen with a higher SPF and three stars may give more UVA protection overall than a low SPF cream with four stars.

...With a valid "use by" date Most sunscreens have a shelf life of two to three years. So you can use last year's left-over sunscreen provided it's been kept in a cool place.

... You can afford The cost of sunscreen does not reflect how effective it is, according to Cancer Research UK. All types are tested and cheaper brands are just as effective if used properly.

Best Buys in a recent Which? survey included "exceptional value" products: Wilkinsons Wilko Sun Protection System Moisturising Sun Lotion at £2.69, Sainsbury's Sun Protect Lotion at £3 and Asda Sun System also £3.

All only live up to their protective promises if applied correctly. You need to use a lot to get the SPF protection indicated on the bottle. Manufacturers use 2mg for every square centimetre of skin when testing the SPF. This means the average adult should use roughly one-sixth of a 200ml bottle to cover the body. Using half the recommended amount gives just a third the level of protection. The Which? survey found that most adults typically use only a quarter to a half of what they should.

Which? also reported that three sunscreens - Malibu High Protection Lotion; Tesco Sun Protection Medium and Marks & Spencer Sun Formula Lotion "twice failed to provide a minimum average SPF of 12.5 in our tests". But all three manufacturers disputed the Which? findings, insisting that they were within specification according to independent tests.

Experts are reluctant to recommend "once a day" products that claim to be resistant to water, perspiration and friction. Cancer Research UK says they may not protect against UVA rays. It says that if consumers are concerned about any claims, they should make sure the product has been tested to standards set by the European Toiletry and Perfume Association by checking the package insert or contacting the manufacturer. This test is widely used by manufacturers although not a legal requirement.