[b]Heathrow airport has asked airlines to halve the number of passengers they fly into the airport next week to try to minimise disruption caused by a strike.

Its operator BAA warned of "gridlock" and said passengers could face 12-hour delays on Wednesday when immigration officers go on strike over pensions.

BAA said it was holding talks with airlines and the UK Border Agency.

PM David Cameron said it was clear there would be an impact at ports and airports, but borders would be secure.

"At the very least there will be longer queues and people will have to wait longer at borders," his spokesman said.

He added the government was still working on contingency plans and gathering information on the impact of the strikes.

'Held on aircraft'

Virgin Atlantic said it was "very concerned", adding it would allow passengers booked on inbound flights on Wednesday to rebook for travel up to four days earlier or later.

BA said it was doing everything it could to protect its customers and they could switch flights free of charge.

BMI said it planned to operate as normal and was also working to minimise disruption, while Cathay Pacific urged its passengers to postpone and rebook their flights.

In a letter to all airlines operating into Heathrow, chief operating officer Norman Boivin said: "The delays at immigration are likely to be so long that passengers could not be safely accommodated within the terminals and would need to be held on arriving aircraft.

"This in turn would quickly create gridlock at the airport with no available aircraft parking stands, mass cancellations or departing aircraft and diversions outside the UK for arriving aircraft." [/b] http://www.bbc.co.uk/news/uk-15884527