The Government is set to announce the fate of plans for a third runway for Heathrow on Thursday.
There had been speculation that a decision on the £9 billion airport expansion was being put off again amid strong opposition from Cabinet ministers and dozens of Labour backbenchers.
However, Transport Secretary Geoff Hoon is now understood to be preparing to make a statement to MPs on Thursday.
The news is likely to anger rebel MPs, who believed Gordon Brown had promised to meet to discuss their concerns in detail before any announcement.
The Government has backed the third runway in principle since 2003, and was widely expected to give the project the green light in December.
Instead Mr Hoon insisted he needed "more time" to assess the environmental impact, and delayed the decision until this month.
Martin Salter, Labour MP for Reading West and a leading opponent of the expansion, said: "It's looking bad. I am expecting a decision tomorrow. I am expecting it to be the wrong decision, with the runway going ahead.
"There will be attempts to sweeten the pill, but it is difficult to conceive of measures that can mitigate the environmental effect of increasing flights out of Heathrow, over one of the most densely populated parts of England, by 50%."
Mr Brown signalled at PMQs that the Government would not seek parliamentary approval if the expansion was endorsed. However, the Tories and Lib Dems intend to force an indicative Commons vote on the issue - which could prove deeply embarrassing for Mr Brown as 49 of his MPs have publicly expressed opposition.
There will also be a full planning inquiry.