By William James

LONDON (Reuters) - Britain's anti-European Union UK Independence Party elected its former chairman Paul Nuttall as leader on Monday, seeking to overcome months of internal turmoil and capitalize on its successful Brexit campaign.

Nuttall, an elected member of the European parliament since 2009, will take over from UKIP's talismanic former leader Nigel Farage, who stood down in June after achieving his decades-long ambition of seeing Britain vote to leave the EU.

While Farage has gone on to become a high-profile ally of U.S. President-elect Donald Trump since the referendum, UKIP has struggled to build on the anti-establishment sentiment it harnessed during the Brexit campaign.

Nuttall, who campaigned on his ability to build the party's support in the north of England and unite its factions, said the party had a duty to Brexit voters to ensure Prime Minister Theresa May did not water down the terms of Britain's EU exit.

"The country needs a strong UKIP more now than ever before because if UKIP cease to be an electoral force then there will be no impetus on Theresa May and her government to give us real Brexit," he said after winning 62.6 percent of the vote in a ballot of party members.

The 39-year-old former history lecturer from Liverpool has served as party chairman and latterly as deputy leader to Farage - whose popularity has, since the referendum, threatened to eclipse UKIP's political purpose.

Speaking on stage before Nuttall's victory, Farage claimed credit for Trump's surprise U.S. election win, saying the anti-establishment message the Brexit vote sent had propelled the Republican to victory, and was set to spread across Europe.

"UKIP's success in this referendum that says to people that normally who don't bother to vote because they assume they're going to get beaten by the establishment ... actually if you go out there and you turn out, this rotten, liberal establishment can be beaten," Farage said.

Nuttall will take control of a party deeply divided by bitter personal disputes between leading figures and uncertain of its political role.

Diane James, who was initially elected to replace Farage in September, stood down after just 18 days, saying she lacked support to professionalise the party. The frontrunner to succeed her, Steven Woolfe, quit the party after an altercation with a colleague left him in hospital.

Nuttall said UKIP, which only has one of the 650 seats in parliament, needed to use the momentum behind the shock Brexit vote to oust the Labour Party, currently led by left-wing veteran Jeremy Corbyn, in many of its traditional working-class strongholds across the north of the country.

(Additional reporting by Kylie MacLellan; editing by Stephen Addison)