LONDON (REUTERS) - London could have a new runway more cheaply and sooner if the British government chose Gatwick over Heathrow as the site for airport expansion, the head of the capital's second airport said on Tuesday.

Lawmakers and business leaders agree that Britain needs new runways to help it remain economically competitive but building more capacity around densely populated London is unpopular with voters and a decision on expansion repeatedly pushed back.

Stewart Wingate, chief executive of London Gatwick, said a second runway could be built at Gatwick for 7 billion pounds (S$14.6 billion) compared to an estimated 17 billion pounds to build a third runway at Heathrow, Britain's busiest airport.

"If chosen - and with swift decision making - we are committing today to start work on site in the next parliament," Mr Wingate said at an event in London on Tuesday.

Gatwick's new runway could be operational by 2025, the group added, a year earlier than Heathrow's plan.

Gatwick airport, located in Sussex about 48 kms south of London, is Britain's second largest airport after Heathrow, which is about 28 kms west of London.

Gatwick Airport is owned by a group of international investment funds ultimately controlled by funds managed by a unit of Global Infrastructure Partners (GIP).

GIP retains a 42 per cent controlling stake in Gatwick. Other shareholders are the Abu Dhabi Investment Authority, National Pension Service of Korea, California Public Employees'Retirement System and the Future Fund of Australia.

Heathrow Limited is owned by unlisted Heathrow Airport Holdings which is co-owned by Spanish infrastructure firm Ferrovial and others partners.

A government commission, led by Howard Davies, the former head of the Financial Services Authority, is currently assessing the issue of runway expansion and will make a final proposal on how and where capacity should be extended by the summer of 2015.