Gatwick Airport's £2.2 billion second runway plan could create thousands of jobs and help "kickstart the economy", British Chancellor Rachel Reeves said.
In the privately-financed project, the West Sussex airport will move its emergency runway 12 metres north, enabling it to be used for departures of narrow-bodied planes such as Airbus A320s and Boeing 737s.
This will enable it to be used for about 100,000 more flights a year.
The Chancellor views the plan as a signal of the Government's commitment to back "the builders, not the blockers".
"By slashing red tape and transforming the planning system to get Britain building again we are investing in this country's renewal and building an economy that works for working people," she said.
Ms Reeves is keen to seize on any positive news for the economy as she prepares for her November 26 Budget against a backdrop of sluggish growth and inflation remaining stubbornly above target.
The Gatwick scheme has been given the go-ahead by Transport Secretary Heidi Alexander.
She backed the scheme as a "no-brainer" for economic growth, a UK government source said, suggesting flights could take off from the new full runway before 2029.
The Cabinet minister is satisfied with adjustments made, covering issues such as noise mitigation and the proportion of passengers who would travel to and from the airport by public transport.
It comes after the Planning Inspectorate initially rejected the airport's application and earlier this year recommended Ms Alexander should approve the project if the changes were made.
New commitments include Gatwick's management setting its own targets for the proportion of passengers who travel to the airport by public transport, rather than a legally binding target.
Residents affected by more noise will be able to ask Gatwick to cover the costs for triple-glazed windows.
Homeowners living directly beneath the new flight routes who choose to sell could have their stamp duty and reasonable moving costs paid, as well as estate agent fees of up to 1% of the purchase price.
Gatwick says its plans will create £1 billion per year in economic benefits, and generate an additional 14,000 jobs.
A GUK gvernment source told the PA news agency: "With capacity constraints holding back business, trade and tourism, this is a no-brainer for growth".
"This government has taken unprecedented steps to get this done, navigating a needlessly complex planning system, which our reforms will simplify in future. It is possible that planes could be taking off from a new full runway at Gatwick before the next general election," the source added.
The source said the expansion must be delivered in line with climate change commitments and meet strict environmental requirements.
Local campaigners opposed to expansion are concerned about the impact on surface transport, noise, housing provision and wastewater treatment, but the airport insists it has conducted "full and thorough assessments" of those issues.
CAGNE, an umbrella aviation community and environment group for Sussex, Surrey and Kent, said it stands ready to serve a judicial review funded by residents and environmental bodies.
"We know this government cares little for the environmental impact aviation is having on our planet and Gatwick's neighbours, but not to demand that Gatwick pays for the infrastructure, the onsite wastewater treatment plant, and noise impact is unlawful in our book," the group said.
The UK government's backing of a third runway at Heathrow Airport in its bid to grow the economy has also drawn criticism from environmental groups and opposition politicians.
