Four London councils wrote to Prime Minister Theresa May this week warning her she would face a raft of legal challenges if the expansion of Heathrow goes ahead, as speculation grows that the government will back the bid in the next two weeks.

The South London Partnership of Richmond upon Thames, Merton, Kingston and Croydon councils argues Gatwick would have lower environmental impacts, lower taxpayer costs and fewer legal barriers.

Epsom and Ewell MP Chris Grayling remained tight-lipped on a decision over whether to expand Heathrow airport in his first Conservative Party Conference speech as transport secretary last week.

He is expected to announce a decision on whether an additional runway will be built at Heathrow or Gatwick airports on Tuesday, October 18.

Chair of the South London Partnership, Merton leader Councillor Stephen Alambritis said: “The South London Partnership boroughs stand ready to work with the Government, the Mayor, Gatwick and other partners to maximise the benefits of a new runway both in terms of stimulating additional economic growth in our area and by providing a skilled workforce to support other areas of growth.

“One thing in particular on which we want to contribute is ensuring the transport links to Gatwick and connectivity more widely, including into our area, central London and with other key corridors, are developed to support the full potential of airport expansion.

“Together with our neighbouring boroughs, we urge Ms May to make the right decision. Choose Gatwick.”

Mr Grayling said he would take his time over a decision on building an additional runway during his speech at the Conservative Party Conference on October 3.

During a speech in which Mr Grayling also prioritised plans for HS2 and slammed the RMT union over the Southern strikes, he said: "It's the responsibility of the Secretary of State if he's going to be involved in a decision like this to play devil's advocate a bit, to ask difficult questions, to really understand the strengths and weaknesses and that is what I've been doing.

"We have three very good proposals.

"Any one of them could benefit to the UK.

"All of them have issues in question around them."

Mrs May’s own local council of Windsor and Maidenhead meanwhile threatened to spend up to £50,000 on a judicial review if a third runway is built at Heathrow.