Suspicious passengers who might otherwise be stopped at Border Control at airports are being “waved through” by military personnel standing in for striking workers.

Two Border Force staff members told Sky News that passengers were being waved through to avoid queues during strikes and that military personnel do not have the power to stop or detain people.

Members of the Armed Forces are providing cover for public services during strikes over winter.

One Border Force officer at Manchester Airport said several members of staff told them that arriving passengers who would normally be questioned are being “waved through in order to avoid queues building up amid strikes”.

They added: “This order is said to have come from management at Manchester Airport. This would mean that people who are potentially unlawfully entering the UK/wanted by the authorities or police/on a watch list/previously refused entry are entering the UK unchecked.”

Around 1,000 Border Force staff in the Public and Commercial Services (PCS) union are striking over pay and conditions from 23 December to Boxing Day.

A Border Force staff member at Heathrow Airport told Sky News that the army on immigration control “can’t stop or detain people” as they cannot issue a form known as an IS81.

The form gives immigration officers the authority to detain people for further questioning.

The staff member added: “Our job is to protect the population and the British public, to protect jobs, people from harm.

“Basically the vast majority of the job can’t be done. I have the information from multiple people. If you cannot issue an IS81, you cannot stop someone. All you can do is let them through.

“Managers left managing the control is that unless there is direct evidence of criminality, they are not to stop them. People who are coming in to work illegally, live illegally, study illegally – and that’s not criminal, it’s an immigration issue. Unless you’re aware that this person is a hit on the computer system, wanted by the police, you can’t hold anybody up.”

Mark Serwotka, PCS general secretary, said: “No one’s being stopped because the government has adopted a sticking plaster approach to this problem.

“We warned before the strikes started that military personnel with five days’ training wouldn’t be able to do the jobs of experienced, professional Border Force officers.”

A Home Office spokesperson said it has “robust plans in place to minimise any delays, passengers should be prepared for disruption and take action to plan ahead”.

A Manchester Airport spokesperson said: “To be absolutely clear, we as the airport operator are not involved in the immigration process… to our knowledge, the immigration process is operating as normal.”