Theresa May will reportedly face a snap by-election after her government gave the green light to a third runway at Heathrow Airport today (25 October). Richmond Park MP Zac Goldsmith is expected to quit the House of Commons.

"He will hand the chancellor his resignation from the Commons on Tuesday afternoon if he has to," a source close to the environmentalist told The Sun. The former mayor of London candidate has been a long-time opponent of expanding Heathrow Airport.

Goldsmith, who was first elected to parliament in 2010, told IBTimes UK last week: "Heathrow has always been the default position of successive governments because the company used to be a monopoly with total access to government, and many of those relationships continue today.

"But in addition to the noise, cost and pollution, a green light for Heathrow would mean more years of dithering and delay, and for that reason there is still a strong chance it will be rejected."

He also failed to rule out running as an independent for the Richmond Park seat, which could cause worry inside Conservative Party HQ after the party's majority was dramatically slashed at the Witney and West Oxfordshire by-election last week.

Goldsmith currently holds a majority of more than 23,000 over the Liberal Democrats.

Transport Secretary Chris Grayling will announce to MPs whether the government is supporting the expansion of Heathrow or Gatwick Airport this afternoon.

His House of Commons statement will follow a meeting of a cabinet sub-committee this morning, where a decision will be made.

Number 10 said May will allow ministers to express "personal views" for a "limited time" on whatever decision the government makes.

The leeway on cabinet collective responsibility will enable Foreign Secretary Boris Johnson and Education Secretary Justine Greening to publicly protest if Heathrow gets the green light.

Parliament will have a final say on the issue, with a vote now expected in the winter 2017/18. The Airports Commission, chaired by Sir Howard Davies and published in July 2015, backed a third runway at Heathrow.

Richmond Park GE2015 result