Mouthwash can kill coronavirus within 30 seconds of being exposed to it in a laboratory, a scientific study has found.

The preliminary result comes ahead of a clinical trial into whether using over-the-counter mouthwash could to reduce the levels of Covid-19 in a patient's saliva.

The Cardiff University report said that mouthwashes containing at least 0.07 per cent cetypyridinium chloride (CPC) showed "promising signs" of combatting the virus.

The report - called The Virucidal Efficacy of Oral Rinse Components Against SARS-CoV-2 In Vitro - is yet to be peer reviewed.

However, it supports results from another study published last week that found CPC-based mouthwashes are effective in reducing Covid's viral load.

The latest test was carried out by scientists at the university's laboratory and mimicked the conditions of a person's naso/oropharynx passage using mouthwash brands including Dentyl.

A clinical trial will next examine how effective mouthwash is in reducing the viral load in the saliva of Covid-19 patients at the University Hospital of Wales in Cardiff, with its results due to be published in the first part of 2021.

Dentyl is the only UK mouthwash brand to take part in the 12-week clinical trial, which is led by Professor David Thomas from Cardiff University and titled: "The measurement of mouthwash anti-viral activity against Covid-19".

Dr Thomas said: "Whilst these mouthwashes very effectively eradicate the virus in the laboratory, we need to see if they work in patients and this is the point of our ongoing clinical study.

"It is important to point out the study won't give us any direct evidence on viral transmission between patients, that would require a different type of study on a much larger scale.

"The ongoing clinical study will, however, show us how long any effects last, following a single administration of the mouthwash in patients with Covid-19."

He added: "Although this in-vitro study is very encouraging and is a positive step, more clinical research is now clearly needed.

"We need to understand if the effect of over-the-counter mouthwashes on the Covid-19 virus achieved in the laboratory can be reproduced in patients, and we look forward to completing our clinical trial in early 2021."

Dr Nick Claydon, a specialist periodontologist, said he believed the research was "very valuable".

He said: "If these positive results are reflected in Cardiff University's clinical trial, CPC-based mouthwashes such as Dentyl used in the in-vitro study could become an important addition to people's routine, together with hand washing, physical distancing and wearing masks, both now and in the future."