David Cameron is poised to quit as an MP if Ed Miliband becomes PM, his allies have sensationally revealed.

Friends of the PM have told the Sunday Mirror that Mr Cameron “could not stomach” five years as a backbench Tory MP if Labour wins the general election next year.

They expect Mr Cameron to quit as an MP within 18 months of an election defeat, triggering a by-election for his super-safe seat of Witney.

If Ed Miliband gets the keys, will David Cameron quit?

His departure would pave the way for Mr Cameron to command an estimated income of more than £5 million a year in directorships and speeches – making him £25 million over a five-year parliament.

Standing down as MP would also allow Mr Cameron to work for a range of potentially controversial clients without having to declare his jobs and income for all to scrutinise in the Register of MPs’ Interests.

Among those tipped as a successor for his Oxforshire constituency is London Mayor and wannabe PM Boris Johnson who has shrugged off speculation that he will try to return to Westminster before the 2015 election.

A senior Tory source disclosed to the Sunday Mirror: “There is no way Cameron will stomach five years on the Opposition benches if Miliband wins the election.

“If Labour in 2015, We’d expect David to quit as an MP within a year to 18 months after ensuring an orderly handover to the next Tory leader – whoever he or she may be.

“David has a wife and three young kids. He’ll want to spend more time with them and to get out there and make some serious cash”.

One of his and wife Sam’s first acts after leaving No10 is expected to be a new home. They are likely to leave their £3m terraced home in North Kensington for a “more secure” central London mansion.

Mr Cameron, aged 47, will have served almost a decade as Tory leader by the general election, expected in May 2015.

As an ex-PM, he would command huge fees for public appearances and up to £250,000 for a single speech.

Unless the Lib Dems hold the balance of power in a future Labour-led coalition, Lib Dem leader Nick Clegg is also likely to quit as an MP rather than serve five years as a backbencher, according to party sources.

If Mr Cameron does go, Boris Johnson would be the choice of many Oxfordshire locals to succeed him.

As the former MP for Henley, the ambitious London Mayor has strong links in the area and is hugely popular with grassroots Tories.

Allies of Mr Cameron said the PM was keen to avoid the problems faced by Gordon Brown who has remained a Scottish MP since leaving Number 10 in 2007.

Mr Brown has come under fire for earning a fortune from speeches – even though all the money goes towards the costs of running his office and the charity work he does with wife Sarah.

When Tony Blair was succeeded by Mr Brown as PM in June 2007, Mr Blair immediately became Envoy of the Quartet on the Middle East and stood down as Sedgefield MP only a month later.

Mr Blair went on to earn a fortune as he Cherie built up a family property portfolio worth £25 million.

Former Tory PM Sir Major remained an MP until 2001 after Tories were crushed in the 1997 election.

After resigning immediately as Tory leader, Mr Major went to watch his beloved Surrey cricket team at the Oval at the start of his money-spinning second career.

The former banker and failed bus conductor soon joined the advisory board of the Carlyle Group which manages the assets of the super-rich and joined the lucrative lecture circuit.

Before the MPs’ expenses scandal in 2009, MPs and ex-PMs were not forced to declare full details of their earnings outside Westminster. So, Sir John and his predecessor Baroness Thatcher escaped scrutiny of their income.