Zac Goldsmith plans to quit the House of Commons over the government's decision to back a third runway at Heathrow Airport. The Richmond Park MP apparently intends to tender his resignation to the constituency's Conservative association today (25 October).

"Zac has contacted the association to let us know that he intends to honours his pledge to resign and force a by-election in Richmond Park," an email to Richmond Park Tories obtained by The Huffington Post reads.

The dramatic move comes before Transport Secretary Chris Grayling addresses MPs this afternoon.

The minister is expected to explain a cabinet sub-committee voted in favour of expanding the West London site in Downing Street this morning.

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."

The environmentalist and former Mayor of London hopeful currently holds a majority of more than 23,000 over the Liberal Democrats.

If he ran as an independent candidate, Goldsmith could split the Tory vote, a worrying move for May after the Liberal Democrats were able to slash the Conservatives' majority at the Witney and West Oxfordshire by-election last week.

Parliament will have a final say on the issue sometime in winter 2017/18 following a public consultation.

But Foreign Secretary Boris Johnson and Education Secretary Justine Greening will be able to protest against a Heathrow expansion after Number 10 said ministers can express "personal views" for a "limited time".

The SNP backs a third runway at Heathrow, while Jeremy Corbyn is expected to give Labour MPs a free vote on the issue. The Greens and Liberal Democrats oppose the expansion. Labour's Mayor of London Sadiq Khan is opposed to the move.