England’s hotel quarantine rules allowing travellers to leave their rooms for fresh air are “very risky”, an Australian epidemiologist has warned.

Professor Michael Toole, from the Burnet Institute in Melbourne, Victoria, suggested England could learn from his country, where preventative measures initially focused on stopping the spread of coronavirus by large droplets but had to be strengthened.

He told BBC Radio 4’s Today programme that the precautions – such as wearing surgical masks, keeping people in their room and using hand sanitiser – did not prevent airborne transmission.

Prof Toole said there have been Covid-19 cases in the city where an infected guest opened their room door and “with the positive pressure this kind of fog of virus went out into the corridor, travelled down and infected hotel staff”.

Asked for his views on people being allowed to leave their rooms in England’s quarantine hotels while accompanied by guards, he said: “We’ve learnt that that is a very risky procedure.”

The state of Victoria has entered a third lockdown after an outbreak of cases thought to be linked to a quarantine hotel.

Australia’s borders are closed but those who can travel, and who are not exempt from quarantine rules, have to stay in a hotel for 14 days.

UK nationals or residents returning to England from 33 “red list” countries will be required to spend 10 days in a Government-designated hotel from Monday.

However, the rules are more relaxed than those in Australia, where people are not allowed to leave their rooms.

The BBC said the Government’s official requirements for hotel operators state that security staff can “accompany any of the arrived individuals to access outside space should they need to smoke or get fresh air”.

But the Department of Health denied people will be allowed outside to smoke, though it said it would be up to hotels to decide on exercise rules.

A Government spokesman said: “Those quarantining in their hotels will not be allowed out of their rooms to smoke; hotel staff will have access to regular testing and suitable PPE.”

Downing Street later insisted the restrictions at quarantine hotels are “in line with other countries who are taking this approach”.

Home Office minister Victoria Atkins defended the policy, saying it is “reasonable” to allow travellers quarantining in hotels a “gulp of fresh air”.

She told Today: “The hotel will of course be adhering to all of the very strict measures that we have in place in relation to social distancing and face masks and so on.

“So I think allowing someone a gulp of fresh air, apart from anything else, we know that being outside is less likely to transmit than being inside.

“But I think allowing someone a gulp of fresh air during a 10-day visit in a hotel, with all the very strict measures that we have, I think is reasonable – but of course we will keep these measures under review.”

Ms Atkins added: “We are confident that the measures that we have in place, ready to go on Monday, are strong and that they will help to protect our country against any of these new variants that are being found.”

But Unite the union said it was “deeply alarming” for hotel workers that the guidelines are “far inferior” to those in Australia.

Hospitality organiser Bryan Simpson said: “Once again the Government has been found guilty of prioritising headlines over the safety of workers.

“It must not be ignored that workers are in as great a danger of transmitting the virus between each other as being exposed to it from quarantining passengers.”

He said if improvements are not made immediately the union will “advise our members of their legal right to withdraw their labour if their health is being placed in immediate danger”.

The revelations that the UK’s guidelines for preventing the transmission of Covid are far inferior to those in Australia is deeply alarming for hotel workers.

Travellers from countries on the banned list can only arrive into one of five airports in England.

Guidance states that anyone from one of those countries with a booking that brings them to a different “port of entry” from February 15 must change it to one of those specified.

The accepted entry points are: Heathrow Airport, Gatwick Airport, London City Airport, Birmingham Airport and Farnborough Airfield.

The published guidance states that leaving the room for exercise will only be allowed with special permission from hotel staff or security and is “not guaranteed”.

In Scotland, where all arrivals must isolate, six hotels near to Aberdeen, Edinburgh and Glasgow airports have been block-booked to house travellers quarantining – with a combined total of up to 1,300 rooms available.

The online booking portal for the hotel quarantine system in England went down shortly after it was launched on Thursday afternoon, and is not expected to be up and running again until later on Friday.

Home Secretary Priti Patel told people to “persevere” with the website, telling an LBC radio listener: “I’ve been told it was back up and running this morning so please persevere with this.”

Meanwhile, ministers are reportedly set to discuss a Cabinet Office proposal on Friday to introduce vaccine and testing certificates for future international travel, according to Sky News.

Asked about the reports, a Government spokesperson said: “The UK Government, like most nations, wants to open up international travel in a responsible, safe and fair manner and we continue to be guided by the science.

“We want to ensure there is an internationally recognised approach to enable travel and are working closely with international partners to do so.”