Heathrow airport has been ordered by the Border Force to stop handing out leaflets to passengers acknowledging the "very long delays" at immigration.

Amid increasing anger at the length of queues for travellers arriving at border control, airport operator BAA has tried to defuse tensions with a leaflet apologising for the problems.

It said people arriving in the country "deserved a warmer welcome" and explained how to complain to the Home Office.

But Marc Owen, director of UK Border Agency operations at Heathrow, has told BAA that the leaflets are "inappropriate" and that ministers would take "a very dim view".

In an email obtained by The Daily Telegraph, he said: "The leaflet... is both inflammatory and likely to increase tensions in arrivals halls especially in the current atmosphere. It is inappropriate in that it is not for you to display how to complain on our behalf.

Mr Owen also told BAA to prevent passengers taking pictures in the arrivals hall. Pictures of lengthy queues have been posted on Twitter by frustrated people.

Former transport minister Jim Fitzpatrick, Labour's aviation spokesman, said: "This is a pure cover-up. I can understand people wanting to take pictures of the queues. This is further evidence of Border Force trying to hide the severity of the problem. Passengers need to know how to register complaints and for Border Force to try to prevent them doing so is outrageous."

In a joint statement issued on Sunday, the Border Force and BAA said: "The majority of passengers pass through immigration control quickly but there are sometimes delays at airports for a range of reasons. We think it's important passengers are given the full picture. We will not compromise border security but we will work together to keep delays to a minimum."

London Mayor Boris Johnson has written to Mrs May to express his "serious concern" about the Heathrow problem. He said the difficulties at Heathrow gave "a terrible impression of the UK" and it was unfortunate that the country's main port of entry was "gaining such a poor reputation".

Mr Johnson told Mrs May he was looking forward to "hearing what measures the Home Office and the UK Border Agency plan to take in order to rectify the situation both for the (Olympic) Games and for usual passenger numbers".