Former transport secretary Justine Greening is due to speak out against a third runway at Heathrow for the first time since she was moved from her job in charge of airports.

The Putney MP is to join London mayor Boris Johnson and fellow MP Zac Goldsmith at a “mega-rally” against the airport expansion on Saturday.

Sources close to Miss Greening, now development secretary, told The Daily Telegraph that her position opposing a third runway has not changed and her views are in line with government policy.

Heathrow Association for the Control of Aircraft Noise (HACAN) chairman John Stewart said the number of senior ministers attending the rally “shows the strength of political opposition there is to Heathrow expansion”.

“Heathrow Airport and its allies may still be pushing for a third runway but their task is looking more impossible with every passing day,” he said. “Politicians and the people of London are united against even the thought of expansion”.

Goldsmith, MP for Richmond Park, said he wants ministers to be “left in no doubt that if they give expansion a green light, they will face a campaign on a truly massive scale”.