LONDON (Reuters) - The leader of Britain’s opposition Labour party, Jeremy Corbyn, could step down before the next national election in 2020 if its poor opinion poll ratings do not improve, the head of its biggest union backer said in an interview published on Monday.

Britain's Opposition Labour Party Leader Jeremy Corbyn addresses the Confederation of British Industry's (CBI) annual conference in London, November 21, 2016. REUTERS/Stefan Wermuth

Labour has consistently placed a distant second in opinion polls and a survey by YouGov in December had the party on 25 percent, its lowest since September 2009, versus 42 percent for Prime Minister Theresa May’s Conservatives.

The next parliamentary election is due in 2020.

“Let’s suppose we are not having a snap election. It buys into this question of what happens if we get to 2019 and opinion polls are still awful,” Corbyn supporter Len McCluskey, head of the country’s biggest union and Labour’s largest financial backer Unite, was quoted as saying by the Daily Mirror.

“The truth is everybody would examine that situation, including Jeremy Corbyn and (Labour finance spokesman) John McDonnell ... These two are not egomaniacs, they are not desperate to cling on to power for power’s sake.”

Left-winger Corbyn was re-elected Labour leader in September after a challenge from one of his lawmakers that exposed sharp divisions between the party’s elected representatives and grassroots supporters.

His office did not immediately respond to a request for comment on McCluskey’s remarks.

May, appointed prime minister in July last year after Britain’s vote to leave the EU forced the resignation of David Cameron, has said she does not intend to hold an early election.

But Labour’s poor poll ratings and a court battle over whether parliament’s approval is needed to begin EU divorce proceedings have increased speculation she could seek to boost her slim majority in parliament by calling a snap vote.

Corbyn has repeatedly said Labour is ready to fight an early election.

His party faces an upcoming electoral test after lawmaker Jamie Reed, a vocal critic of Corbyn, said last month he would step down at the end of January. The area in northern England that Reed represents voted strongly in favor of Brexit.

In a December election for a vacant Conservative-held parliamentary seat, Labour slipped from second to fourth place.