Three people in WA hotel quarantine have tested positive to a fast-spreading mutated strain of COVID-19 detected in the UK.

Premier Mark McGowan said the three cases are all returned travellers from Britain.

“Three people have been diagnosed with the new UK variant which is a more rapidly spreading variant of the virus, and obviously it is causing havoc throughout England,” he said.

This is the first time the UK strain has been detected in WA’s hotel quarantine system.

But the Premier is confident the disease won’t break through WA’s containment line.

“They’re in hotel quarantine in rooms, the precautions are very strong, and everyone who interacts with them obviously has to adhere to all of the protocols,” he said.

“We are managing those cases and our hotel quarantine system has proven effective in preventing the spread of the virus.”

The Premier has asked the Commonwealth to look at making COVID-19 testing mandatory for international travellers before boarding flights to Australia.

Only one new case of the virus was recorded overnight.

The three mutated cases were previously reported and following routine genome sequencing health officials can now confirm the strain.

Overnight United Kingdom Prime Minister Boris Johnson announced a third national lockdown until February to combat the disease.