The British government is expected to announce its decision on whether to give the go-ahead for a third runway at London's Heathrow Airport at 1230 GMT on Thursday, a Department for Transport spokeswoman said.

The long-awaited decision on the 9 billion pound ($13.46 billion) expansion of the world's busiest international airport will be announced in a statement to parliament by Transport Secretary Geoff Hoon.

The government is expected to give the green light to the third runway, despite intense opposition from environmental campaigners, opposition parties and some members of the ruling Labour Party.

Supporters say the third runway is needed to enable Heathrow to run more efficiently and to cope with expanding air travel.

Opponents argue that the development would increase noise for local residents and push up carbon dioxide emissions, making it harder for the government to meet its goals on climate change.

The Guardian reported on Thursday that the go-ahead for a third runway would be accompanied by plans for a new high speed rail line linking London, Heathrow Airport and Britain's second-largest city Birmingham.

The opposition Conservatives say that, if they win the next general election, due by mid-2010, they would scrap plans for a third runway and would instead build a more ambitious high-speed rail link linking London to northern cities.