The UK economy would be boosted by £21.7bn if the third runway at Heathrow airport were to be built according to the British Chambers of Commerce (BCC).

The business group said that investment in key UK infrastructure projects must not be reduced despite tight public finances, with this being the single largest benefit from the 13 key transport projects that would boost the economy by £85bn.

Lord Adonis, UK transport secretary, said: "Even in tough economic times, we must continue to invest in vital transport infrastructure which benefits jobs, businesses, our economy and the environment."

Both the Labour and Conservative parties have stated that they would cut public spending in order to reduce the budget deficit.

David Frost, BCC’s director general, said: "Transport infrastructure cuts must not become a politically convenient way to slash spending after an election, especially when there are huge savings to be made in far larger budgets, including health, education and welfare.

"Cutting or scrapping plans for regional transport improvements means fewer jobs, and ultimately fewer businesses driving recovery."

The total cost of the infrastructure projects, including Londons Crossrail train link, a third runway at Heathrow airport, as well as road and rail improvements, is estimated at £29.8bn by the BCC.

The public sector would contribute £3.1bn a year for five years, with the private sector making up the remaining £14.3bn.