Left-wing firebrand George Galloway was elected to the UK parliament on Friday after tapping into anger over the Israel-Hamas war in a chaotic by-election marred by anti-Semitism allegations.

Galloway, 69, first became an MP in 1987 and will return to the House of Commons for the first time since 2015 after winning the seat of Rochdale, in northwest England, by nearly 6,000 votes.

The turbulent vote saw the main opposition Labour party withdraw its candidate, Azhar Ali, after he touted a conspiracy theory that Israel had allowed Hamas to carry out its deadly attack on October 7.

Galloway, long accused by critics of stoking community tensions, put the Gaza conflict front and centre of his campaign in Rochdale, which has a 30 percent Muslim population.

"Keir Starmer, this is for Gaza," Galloway, leader of the fringe Workers Party of Great Britain, said in his victory speech, referring to Labour's leader.

"You have paid, and you will pay, a high price for the role that you have played in enabling, encouraging and covering for the catastrophe presently going on in occupied Palestine in the Gaza Strip," he added.

Starmer, tipped by pollsters to become Britain's next prime minister following a general election due later this year, has been reluctant to criticise Israel and only recently backed calls for a ceasefire.

Labour's stance has caused divisions within the party and sparked several frontbench resignations, but pollsters say the centre-left outfit remains on track to oust the ruling Conservatives in the nationwide vote.

- 'Maverick' -

Galloway has been a repeated thorn in the side of Labour since he was expelled from party in the 2000s.

His anti-war rhetoric will now pose a headache for Starmer after he is sworn into parliament on Monday.

But political scientists cautioned against reading too much into the result, in which the country's traditional three main parties failed to finish in either first or second place.

"If George Galloway can all of a sudden manufacture 20-30 clones to stand in the seats with the highest Muslim populations, and generate adequate resources to run a general election campaign, then maybe he can pose Labour a serious threat," said Chris Hopkins of polling firm Savanta.

"But realistically, Galloway is a bit of a maverick, a one-off, and has taken huge advantage of a non-campaign from the established parties in Rochdale."

He grabbed nearly 40 percent of the votes cast -- on a turnout of 39.7 percent -- while a local businessman and independent candidate was the surprise runner-up.

The by-election was triggered by the death of veteran Labour MP Tony Lloyd.

A Labour spokesperson said the party "deeply" regretted that it was not able to have a candidate and apologised to Rochdale residents.

"George Galloway only won because Labour did not stand," said the spokesperson, adding that Galloway "is only interested in stoking fear and division".

"As an MP he will be a damaging force in our communities and public life."

- 'Concerned' -

The Scottish-born Galloway sparked controversy in the 1990s when he visited then-Iraq leader Saddam Hussein, telling him: "Sir, I salute your courage, your strength, your indefatigability."

He then gained international notoriety in 2005 when he was called to testify over Iraq in the US Senate. He was expelled from Labour in part for calling on British troops "to refuse to obey illegal orders" in Iraq.

Galloway, then representing the Respect Party, ousted a Labour MP for a constituency in east London at the 2005 general election. He last represented a seat in Bradford, northern England, from 2012 to 2015.

A spokesperson for the charity Campaign Against Antisemitism said Galloway has "an atrocious record of baiting the Jewish community".

"Given his historic inflammatory rhetoric and the current situation faced by the Jewish community in this country, we are extremely concerned by how he may use the platform of the House of Commons in the remaining months of this parliament."