British holidaymakers visiting the US could be hit with higher air fares and extra security before boarding flights, under new plans for armed US immigration officers to be stationed at UK airports.

The change, which would see transatlantic passengers clearing immigration formalities before boarding an aircraft, is being discussed in Washington and Whitehall with officials understood to be negotiating over the practicalities.

Under the plans airlines could be forced to pay for US security staff and their families to live in the UK, meaning they are likely to pass these extra costs onto passengers travelling from Britain to the US.

Passengers are also likely to be asked to leave more time between turning up at airports before flights, as they will have to undergo questioning by US security in addition to usual checks.