Mouthwash can kill coronavirus within 30 seconds of being exposed to it in a lab, a scientific study indicates.

Scientists at Cardiff University found there were "promising signs" that over-the-counter mouthwashes may help to destroy the virus.

The report comes ahead of a clinical trial on Covid-19 on patients at the University Hospital of Wales.

Dr Nick Claydon said the study could lead to mouthwash becoming an important part of people's routines.

While the research suggests use of mouthwash may help kill the virus in saliva, there is not evidence it could be used as a treatment for coronavirus, as it will not reach the the respiratory tract or the lungs.

Dr Claydon, a specialist periodontologist, said: "If these positive results are reflected in Cardiff University's clinical trial, CPC-based mouthwashes... could become an important addition to people's routine, together with hand washing, physical distancing and wearing masks, both now and in the future."

The university report states that mouthwashes containing at least 0.07% cetypyridinium chloride (CPC) showed "promising signs" of being able to eradicate the virus when exposed to the virus in a lab.

While the report is yet to be peer reviewed, it supports another recent study which found CPC-based mouthwashes are effective in reducing viral load.

Dr Richard Stanton, lead author on the study, said: "This study adds to the emerging literature that several commonly-available mouthwashes designed to fight gum disease can also inactivate the SARS-CoV-2 coronavirus (and other related coronaviruses) when tested in the laboratory under conditions that are designed to mimic the oral/nasal cavity in a test tube.

"This study is not yet peer reviewed and published which means it has not yet been scrutinised by other scientists as is the usual process with academic research. It has now been submitted for publication in a journal.

"People should continue to follow the preventive measures issued by the UK government, including washing hands frequently and maintaining social distance."

A clinical trial will look at whether it helps to reduce levels of the virus in the saliva of Covid-19 patients at the hospital in Cardiff, with results expected early next year.

Prof David Thomas, from the university, said the initial results were encouraging, but the clinical trial would not produce evidence of how to prevent transmission between patients.

"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," he said.

"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."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."