A Which? report this month assessed the standard of cheap sunglasses being sold at a number of high street outlets.
Which? tested 21 pairs of sunglasses priced below £5 from seven high street shops, but claimed 15 breached the British Standard.
Of these, three Asda George sunglasses failed Which? laboratory tests, as did two out of three Marks and Spencer (M&S) pairs, all three Poundland pairs, one out of three Primark pairs, and all three pairs tested from both Sainsbury's and Tesco.
The remaining sunglasses passed, including all three from fashion retailer New Look that were priced below £2.99.
All the sunglasses tested were found to block UV rays but a host of other issues were identified. Among these was a pair of Poundland sunglasses too dark for safe driving and a Primark pair with the wrong prescription level 'which could make vision problems, such as astigmatism, worse', according to Which?
A Poundland spokesperson said its products were compliant with legislation, adding it was 'reviewing the sunglasses and will endeavour to rectify the product should any problems be found'.
Primark, meanwhile, disputed the findings and said it would conduct its own internal review. 'Primark rigorously tests all the sunglasses it sells and ensures that these products meet the required UK and European standards,' a statement said.
Sainsbury's and M&S also said their sunglasses met British safety standards. 'We are surprised and disappointed with the Which? findings,' M&S said. A spokesperson for Sainsbury's added: 'We categorically dispute the findings of Which? on these products.'