Theresa May is coming under further pressure after Labour obtained figures indicating the scale of the relaxation of checks at the UK Border Agency over the summer.

Labour's shadow Home Office team has also published emails suggesting that some passengers entering the country on private jets didn't have their passport checked at all, which would directly contradict a claim made by Theresa May last week that nobody had been "waived through" on entry to the UK.

Earlier the Home Office disclosed that a pilot scheme involving reduced checks on some passports ran at 28 ports and airports in Britain, including both Heathrow and Gatwick. 10 million people entered Britain during the month of August alone. The pilot scheme ran from the end of July until the middle of October.

Last week Theresa May had been unable to tell MPs how widely the pilot scheme had been used.

In an email published by Labour on Monday night, a UK Border official at Durham Tees Valley airport writes about not being “allowed to physically see the passengers” arriving on private jets. The official said the instructions sent from senior management were creating an "unnecessary gap in border security", but their concerns were downplayed in subsequent emails from senior managers, who said their policy of "risk assessment" meant they were "responding proportionately".

The emails discussing this apparent dispensing of the need to check passengers on certain flights go back to March of this year, far earlier than the beginning of the pilot scheme outlined by Theresa May last week.

The Home Secretary had claimed that UK Border officials had exceeded the terms of the pilot scheme authorised by her, and had relaxed passport checks without ministerial approval.

Labour have also claimed that over the summer the terms of the pilot scheme authorised by the Home Secretary were used more than 100 times a week at various points of entry to Britain. Nearly 3 million people, mostly from the EU, arrived into the country every week during that period.

Shadow Home Secretary Yvette Cooper said in her statement on Monday night: "Last week the Home Secretary told us that no one had been waived through without checks this summer. But these documents show passengers on private flights weren't even seen.

"Last week the Home Office wouldn't admit to having figures about how often checks were downgraded. Now we know those figures exist, and that checks were downgraded 260 times in one week alone -- potentially for hours each time."

On Tuesday the suspended head of the UK Border Force, Brodie Clark, will appear before MPs on the Home Affairs committee, to be questioned about the discrepancies between the Home Secretary's response to the scandal and his own statement, issued shortly after his resignation.

Clark was suspended by the head of the UK Border Agency ten days ago. He resigned a few days later and is considering suing the government for constructive dismissal. In his resignation statement Clark claimed he was being made a political scapegoat.