Brits have been warned over mineral-based sunscreens that have failed to provide the level of protection claimed on their packaging.

It comes as the Met Office issued a health warning as a 34C heatwave is set to hit the UK.

Consumer group Which? warned the expensive sunscreens, costing as much as £28, failed tests to see whether they offer the level of protection claimed.

Which sunscreens were tested?

One of the least effective, Clinique Mineral Sunscreen Lotion, which costs £26 for a 125 ml bottle, barely provided a third of the claimed SPF level in tests, according to the testing.

Tropic Skin Shade Cream, costing £28 for 200ml, co-owned by Lord Sugar and former Apprentice contestant Susan Ma, barely provided a third of its claimed SPF30 and also failed tests for UVA.

However, Which? said it was the only brand that had committed to a full re-testing of its product and had ceased sales of it while they waited for the results.

Alba Botanica Sensitive Mineral Fragrance Free, £11.99 for 113ml, which is sold on the high street at Holland and Barrett, also failed both SPF and UVA testing.

Hawaiian Tropic Mineral Protective Sun Milk (£10.50/100ml) passed the Which? UVA testing but also offered significantly less SPF protection than claimed, meaning it failed the tests.

The fifth mineral sunscreen, Green People Scent Free Sun Cream SPF30 at £25.50 for 200ml, which also uses chemical UV filters, passed on SPF protection but failed when it came to blocking UVA rays.

Most high street sunscreens, known as chemical based sunscreens, work because they use ingredients that absorb UV rays, whereas mineral sunscreens physically block ultraviolet radiation using ingredients like titanium dioxide or zinc oxide.

Which? said products needed to pass both SPF and UVA tests to be considered acceptable, so it had labelled all five mineral products that failed its testing as Don’t Buys.

Which? issue advice ahead of 34C heatwave

Natalie Hitchins, Which? head of home products and services, said: “Looking after your skin while enjoying the sunshine is something everyone should do to prevent skin damage and the risk of skin cancer. It’s a massive concern that none of the expensive mineral sunscreens in our tests offered the level of protection claimed on their packaging.

“Our advice is don’t waste your money or take any unnecessary risks – stick to a tried and tested and reliable suncream. We’ve found plenty of highly effective, cheap sunscreens available on the high street so there’s no need to splash out to keep you and your loved ones safe in the sun.”

Edgewell, which makes Hawaiian Tropic, said: “We are proud of the quality and performance of our products and we stand behind their labelling.

“In the specific case of our product Hawaiian Tropic Mineral Protective Sun Lotion Skin Nourishing Milk SPF 30, we firmly disagree with the testing results obtained by Which? Our product was tested using the ISO 24444 method and obtained a SPF result of 34.5.

“In addition, our product obtained results for UVA protection levels that surpass the minimum thresholds required by European regulations currently recognised by the United Kingdom.”