The UK’s plan to tighten its borders against Covid-19 by ordering people to declare why they are leaving the country faces fresh uncertainty after airline staff warned they could not enforce the rules.

Priti Patel, home secretary, announced the policy a week ago as part of a wider package of measures including hotel quarantine for those entering the country from “red list” countries with virulent strains of the virus.

She pledged an increase in the police presence at airports and introduced a new requirement for people to declare their reason for travelling, which should be examined by airline staff at check-in.

But staff at Heathrow, the UK’s busiest airport, told the Financial Times on Friday that they had not been told to check why people were travelling when they check-in.

Ticketing agents said they were not in a position to judge whether a trip was essential and the passenger should be allowed to travel, or if they should be denied boarding.

Aviation executives have also privately expressed concern that airport and airline workers are being asked to effectively act as border agents.

The industry has warned that ground staff should not become involved and that the police should be used to challenge passengers.

The GMB union, which represents staff in the aviation sector said it was “deeply concerned” for its members. “There is currently no oversight from government to make sure travel is only being done for essential reasons,” the union said in a statement.

At the same time airport staff also warned that they were struggling to check the veracity of pre-flight Covid-19 test results, which are now mandatory.

“We are under more pressure than ever due to the increased checks and procedures now in place,” one staff member told the FT. “I’m angry that the government has not done more to make sure travel is genuinely essential.”

Staff have been told to perform what they describe as “cursory” checks on test certificates to check details such as the name matches the passenger’s passport, but said they were unable to tell whether the paperwork was genuine.

The International Air Transport Association, a trade body, has warned that fake Covid-19 test certificates are a growing problem, and that check-in staff had been left to police a bewildering array of often paper documents.

Meanwhile, the government has launched negotiations with hotels to secure up to 28,000 rooms over a month where UK residents returning from red list countries will have to stay for 10 days.

Under the new scheme, which is scheduled to start from February 15, hotels must be near 10 specific airports and ports with private security guards in place to prevent people leaving their rooms.

The arrivals — expected to number 1,425 a day — will each have to pay more than £1,000 for their enforced self-isolation. The measure has been brought in to control the spread of new variants of Covid-19 from countries including Brazil and South Africa.

The government also held a call with the aviation industry on Friday to discuss the logistics for hotel quarantining, with key details such as whether to segregate passengers from “red zone” countries still unclear.

Separately, Downing Street said it had no plans to introduce “vaccine passports” to enable those who have been inoculated against coronavirus to travel abroad.

However, officials privately confirmed that long-term discussions had been taking place for months about how each citizen could have a document in future to prove that they had been vaccinated — to facilitate overseas travel.

A government spokesperson said people should not be travelling unless necessary and pointed to a range of recently tightened border controls including the hotel quarantine policy.

“We’re also going further and the police have stepped up checks, we are introducing a new, managed isolation process in hotels for those who cannot be refused entry and people will also have to declare their reason to travel, which will be checked prior to departure.”