A multi-billion pound energy deal has delivered another blow to the prospects of a Thames Estuary airport being built.

Centrica, the owner of British Gas, has agreed to buy up 3 million tonnes of liquefied natural gas a year from 2014.

This will be taken to the National Grid’s LNG terminal at Grain, the largest in Britain.

The agreement with Qatargas could provide enough gas to meet the needs of around 3 million households.

The facility would have to be moved to make way for an airport, an incredibly complex operation that could cost more than £3 billion.

Grain is one of a number of sites that have been proposed so far, and it is one of the proposals backed by London Mayor Boris Johnson.

Other sites include Cliffe and an airport in the estuary itself.

A decision on whether to build an airport will be made after the next election in 2015.

Mick Rix, the GMB national officer for the transport sector, told The Independent: "This is yet another nail in the coffin for Boris's idea – and nobody supports him.

"Aviation has to be the most secure industry given previous activities by armed groups [the 9/11 terrorist attacks], so I cannot see how the authorities would allow a hub airport to be built over an LNG facility."