"ALARMING" differences in the effectiveness of widely-available reusable masks to deal with Covid-19, has emerged from new research.

Manufacturers and retailers have been urged to up their game on face coverings after a study found that the worst masks only managed to block out a "paltry" seven percent of potentially harmful bacterial particles from penetrating the mask material - allowing 93% to escape.

The study by the consumer organisation Which? concluded that three out of the 15 face coverings Which? tested performed so poorly that they were deemed a ‘Don’t Buy’.

In June, Scots shoppers were warned of the risks of buying face masks from online sites such as eBay, with scammers looking to take advantage of the coronavirus crisis.

Analysis by Scottish tech firm Vistalworks then found a large number of masks for sale which include false claims to be medical grade PPE, and it updated its free online checker tool embedded on the website of Scotland’s national consumer advice service consumeradvice.scot to warn shoppers of the risks.

With face coverings an essential purchase, Which? examined a range of options widely available in places like Asda, John Lewis, Boots, Ocado and Asos, and tested how well they filter bacteria, how breathable they are, and how they fare after multiple washes.

The study found that the best performing face coverings were able to block more than 99 per cent of potentially harmful bacterial particles from penetrating the mask material - similar to the standard of surgical masks.

At the bottom of the table and earning the lowest scores overall were a face covering from Termini8 sold at Lloyds Pharmacy (£2), one from Asda (£3) and one from Etiquette (£3), which is sold at Superdrug.

Which? said all were lightweight and breathable as they were made with only one layer, but this affected their ability to filter potentially harmful particles, earning each mask only one star out of five in this category.

The lab tests revealed that masks with multiple layers are much more effective than single layer masks at filtering particles.

They also revealed that almost all of the face coverings got better at filtering particles after being washed. Face coverings were re-tested after five hot wash cycles, and most improved, due to the fibres compressing.

Just two of the products got Best Buy status. The NEQI reusable face mask (£15 for 3), which is available from retailers including Boots and Ocado as well as Bags of Ethics Great British Designer face coverings (£15 for 3), available at Asos and John Lewis. They were both considered "comfortably breathable without compromising on filtration".

Which? found that there was a clear trade off between breathability and how effective the mask was at filtering potentially harmful particles.

READ MORE: Coronavirus -  What you need to know about choosing a face mask

In fact, the fabric masks that scored five out of five for filtration were also those that scored the lowest for breathability.

If a face covering isn’t breathable, it can get damp more quickly with condensation from trapped breath and might encourage people to adjust or remove their mask, especially if they wear glasses.

Which? is urging manufacturers to use these findings as a basis for improving their products, while retailers should seek to ensure they are selling products that will effectively filter out potentially harmful particles. In the meantime, the consumer champion is encouraging consumers to research the best available options for themselves and their loved ones before making a purchase.

Natalie Hitchins, Which? head of home products and services, said:“With face coverings now such an important part of daily life, they not only need to be durable and comfortable, but also provide effective filtration from harmful particles in order to keep us and others safe.

“Our results prove that there is a huge difference in quality between reusable masks sold in stores around the country and online. We would urge manufacturers to use our findings to up their game and improve their products - Until then it is worth taking time to research the best option for yourself and your loved ones.”

ROR from Lloyds Pharmacy - seller of the Termin8 mask said: “We take the quality and efficacy of the products we sell very seriously and work with our suppliers to ensure they comply with UK regulations and standards. We have confirmed with the supplier of the Termin8 mask in question that it is compliant with all necessary requirements as set out by the Department for Health & Social Care and the British Retail Consortium, for use as a face covering in numerous public settings as required by UK law.”

Superdrug disputed the testing methods and said it was "disappointed" that the Etiquette mask was given a ‘Don’t Buy’ rating because it had been tested against the EN 14683 standard for surgical masks and the CEN Workshop Agreement which is not an official standard. This product was clearly retailed as a fabric face covering and not a surgical mask – designed to help the wearer reduce the spread of a cold or virus, as per Government guidelines.”

Asda added: “Product safety is our key priority and all of our George face coverings comply with and British Retail Consortium guidance and the Office for Product Safety and Standards. The covering that featured in this review was produced before the CWA17533 guidelines were published and is no longer on sale.”