BUILDING an extra runway at Gatwick will cause the Brighton Main Line to go into “complete meltdown”, according to a group of campaigning MPs.

MPs from the Gatwick Coordination Group have written to rail minister Paul Maynard warning of the “devastating impact” expanding Sussex's biggest airport would have on the “already beleaguered” Southern rail service.

The MPs, including Mid Sussex’s Sir Nicholas Soames, claim that a £10 billion rail network upgrade would be required to cope with up to 140,000 additional rail trips per day.

Gatwick bosses dismissed the concerns claiming the station would be “rail and road ready” to meet any increase in demand from another runway by 2020.

The Sussex airport remains locked in a battle with rival Heathrow over expansion plans more than a year after the Airports Commission recommendation of a Heathrow expansion.

Ministers are expected to be given a free vote when Parliament comes to make a decision on the two rival proposals although a possibility that both airports could be expanded is also being mooted.

Former transport minister Theresa Villiers said this week that Heathrow’s expansion was "undeliverable" and that Gatwick is the better option to expand.

But MPs in the GCG, which also includes Crawley MP Henry Smith, Wealden MP Nus Ghani and Arundel and South Downs and Arundel MP Nick Herbert, warn that this summer of misery for train passengers would be a “small sign of things to come” if Gatwick expanded.

The MPs also criticised Gatwick for not committing a single penny towards any cost of improving rail infrastructure “leaving commuters and taxpayers to foot any bill”.

Group chairman Crispin Blunt said: “The Brighton Main Line is already operating over capacity and is one of the busiest and worst performing rail lines in the country.

"This summer’s misery on the railways highlights the vulnerability of the rail network to severe disruption and the need for new capacity to cope with rising commuter demand.

“The last thing the Brighton Main Line and its users need is extra burden of an ill-conceived Gatwick expansion, rail services would go into complete meltdown.”

A Gatwick spokesman said: “The Airports Commission itself concluded road and rail improvements already underway or planned will more than meet the demand a second runway would create.

"Indeed, Gatwick will be road and rail ready for a second runway by 2020 which is five years before a new runway can be operational.

"With increased investment and projects already underway, Gatwick’s rail capacity is set to double by 2020, boosting growth and benefiting local rail users who can expect a significantly improved service in the coming years.”