Heathrow third runway campaigners today insisted the fight against expansion was just beginning as the Government appeared set to give the go-ahead.

Activists have already planned a flash mob at Terminal Five this Saturday, where hundreds of protesters will gather wearing red T-shirts with the slogan 'Stop Airport Expansion'.

Gordon Brown is widely predicted to give expansion the go-ahead later today, following a week of twists and turns.

He was expected to approve plans for a third runway and sixth terminal, allowing the number of flights to increase nearly 50 per cent to 702,000-a-year by 2030.

It is unclear whether proposals to end runway alternation and segregated mode, and to scrap the Cranford agreement - which campaigners claim would be 'devastating' for local residents - will also be approved.

Christine Shilling, of No Third Runway Action Group (NoTRAG), said the Government had ignored the views of 70,000 people who took part in the consultation process last year and vowed to continue campaigning until the 'bitter end'.

"This is not the end," she added. "It is simply the end of the beginning."

Hounslow Council revealed today how its survey of 2,000 west London residents showed a massive 96 per cent were opposed to expansion.

Cllr Barbara Reid, the council’s aviation chief, said the Government should 'realise it is beaten and give up'.

She added that the council was likely to launch a legal challenge, backed by London Mayor Boris Johnson, on the grounds Heathrow is already breaching a raft of guidelines on pollution and noise.

Activists, who have spent the last few months training in militant camps, are also expected to step up their campaign of direct action.

Should the Government approve a third runway, it is unlikely to be ready before 2019.

Mr Brown has promised a debate in Parliament, which will be followed by a lengthy planning process, before work can even begin.

Ministers say expansion will only be allowed if EU pollution targets are met and there is no increase in the noise suffered by residents living under the flight path.

Airport bosses, who say a third runway is vital for the long-term health of the British economy, insist this can be achieved by developing quieter, cleaner planes despite the scepticism of environmentalists.