DURHAM Tees Valley airport has strenuously denied that safety was put at risk due to the alleged relaxing of immigration checks.

Last night a leaked email from a UK Border Agency official at Durham Tees Valley stated that managers were not allowed to physically see the passengers on private jets, saying it was at odds with national policy and is creating an unnecessary gap in border security.

Labour published the emails from the official who also said relaxed checks brought in in March were creating a situation "where we are not able to secure the border as robustly as we would like to, for no justifiable reason".

Managers replied that "there was a new national GA (general aviation) strategy being rolled out which was consistent with national policy".

However, this afternoon, Durham Tees Valley airport manager Shaun Woods, said: “I want people to be absolutely clear that, the decisions on how to implement border controls are a matter for the UK Border Agency with whom we work very closely.

"I also want people to know that any suggestion passengers or crew could pass through the airport without undergoing the appropriate checks required by the UK Border Agency is plain wrong."

The UKBA also issued a strong denial last night, saying: "It is not true that we don't carry out passport and warnings index checks on private flight passengers and will deploy officers to airfields where we have concerns."

Government estimates show there are between 80,000 and 90,000 private jet flights every year.

Figures released by Labour also showed Mrs May's pilot scheme to relax border controls - referred to as level two checks - was used 260 times in the sixth week of the trial, the week ending September 16.

This compared with 100 times in its first week and 165 in week nine, ending October 9.

The figures were revealed in leaked UKBA documents encouraging staff to use the new level two controls whenever it was possible to do so.

It also emerged over the weekend that coach passengers have been allowed into the UK without being properly checked by border staff for four years.

Shadow home secretary Yvette Cooper said: "This is startling new information about the scale of the borders fiasco.

"Ten days on there are even more questions than answers about what on earth was going on at our borders this summer.

"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."

She called for Mrs May to release the full facts and figures immediately, saying "as long as she refuses to do so, people will think she has something to hide".

UKBA chief Brodie Clark resigned last week to pursue a case of constructive dismissal which could lead to a payout of up to £135,000 after Mrs May was accused of "hanging him out to dry" over the controversy.

She repeatedly told MPs that Mr Clark reduced the checks without ministerial approval.

Mrs May said she authorised piloting the easing of some border checks on EU travellers over the summer, partly to reduce queues.

But she insisted Mr Clark went further, scrapping key checks against a Home Office database of suspected terrorists and illegal immigrants without ministerial approval - all after she had already rejected his suggestions.

Meanwhile, the Home Office Permanent Secretary Dame Helen Ghosh said she was currently unable to confirm that no minister or official at the Home Office knew that border checks had been relaxed beyond those authorised.

In a letter to the Commons Home Affairs Select Committee, she said: "This is one of the matters being covered by John Vine's investigation."

In a second letter to the same committee, Mrs May also confirmed the pilot scheme, which was available to all ports, was used at both Heathrow and Gatwick airports, and at Calais.

It was also used at the ports in Aberdeen, Belfast, Bournemouth, Bristol Airport, Cardiff, Coquelles, East Midlands, Edinburgh, Exeter, Glasgow, Harwich, Leeds Bradford, Liverpool, London City, Luton, Manchester Airport, Newcastle, Newhaven, Norwich, Plymouth, Poole, Portsmouth, Prestwick and Stansted.

Provisional figures also showed there were ten million journeys through the UK's ports in July 2011, and another 10.2 million in August 2011 - the summer peak periods at the centre of the border checks row.