Which? tested 21 pairs of sunglasses from seven high street shops and found that 15 failed key lab tests, breaching the British Standard.
You might not expect a pair of £5 sunglasses to last forever, but you wouldn't expect a supposed bargain to potentially worsen your eyesight, cause double vision or headaches.
The sunglasses on test were bought from George at Asda, Marks & Spencer, New Look, Poundland, Primark, Sainsbury's and Tesco.
All the sunglasses blocked UV rays, but a Poundland pair was mislabelled, leaving a wearer unaware that the lenses were too dark for safe driving.
Although two out of three Primark pairs passed our tests, the one that failed had the wrong prescription level which could make vision problems, such as astigmatism, worse.
New Look was the only store where all three pairs passed the Which? tests with flying colours.
Which? health expert Joanna Pearl said: 'While these problems would not cause long-term vision damage, some of them would be unpleasant for the wearer and could even compromise their safety. Glasses must comply with the British Standard they clearly claim to meet on the label.'
We will be sending the worst results to Trading Standards.Asda, M&S, Primark, Sainsbury's and Tesco all confirmed that their sunglasses are tested to British Standards.
M&S, Primark, Sainsbury's and Tesco rigorously disputed Which?'s findings, with M&S expressing their surprise and disappointment.
Asda, Poundland and Primark will be investigating immediately.
If you're buying sunglasses make sure you do the following checks:
Here are our results for each pair we tested and the standards they failed on:
|Asda (George) pair 1||£4.00||Fail. Both lenses were darker in some places than others, letting in different amounts of light across the lens|
|Asda (George) pair 2||£5.00||Fail. The left lens was darker in some places than others, letting in different amounts of light; there was a scratch on the right lens. This pair also had a semi-circular 'imprint' or undulation in the middle of the left lens which could distort vision.|
|Asda (George) pair 3||£2.50||Fail. There was a pit in the left lens, indicating poor surface quality|
|Marks & Spencer (M&S) pair 1||£5.00||Fail. Both lenses were darker in some places than others, letting in different amounts of light across the lens|
|M&S pair 2||£5.00||Fail. Both lenses were darker in some places than others, letting in different amounts of light across the lens|
|M&S pair 3||£5.00||Pass|
|New Look pair 1||£2.00||Pass|