LONDON (Reuters) - After militants killed seven people and injured 48 in London, British Prime Minister Theresa May resumes campaigning on Monday just three days before a national election which polls show is much tighter than previously predicted.

May said Britain must be tougher in stamping out Islamist extremism after three knife-wielding assailants rammed a van into pedestrians on London Bridge and stabbed others nearby.

Following the third militant attack in Britain in less than three months, May said Thursday’s election would go ahead and that Britain had been far too tolerant of extremism.

“Violence can never be allowed to disrupt the democratic process,” May, who served as interior minister from 2010 to 2016, said outside her Downing Street office on Sunday.

Islamic State, which is losing territory in Syria and Iraq to an offensive backed by a U.S.-led coalition, said its militants were responsible for the attack, though it is unclear what links the attackers had to the group.

London police chief Cressida Dick said that while some of the recent attacks in Britain had international links, they had a largely domestic center of gravity.

May said the three recent attacks, which have claimed at least 34 lives, are not thought to be connected.

But she said Britain was under threat from a new breed of crude copycat militants who might not have spent years plotting or even been radicalized online.

Deadly attacks by Islamist militants in Paris, Nice, Brussels, Berlin, Manchester and London over recent years have shocked Europeans already anxious over security challenges from mass immigration and pockets of domestic Islamist radicalism.

In an early morning raids in east London, British counter-terrorism police detained more people on Monday. Police arrested 12 people in the Barking district of east London following the attack, though one was later released.

Police have not released the names of the attackers and British newspapers refrained from identifying the men.

“This has been a truly ghastly few weeks,” said London police chief Dick, who said the spell of recent attacks was unprecedented in her working experience which began in 1983.

May was due to chair a meeting of the government’s emergency response committee on Monday.

SHADOW OF ATTACKS

It was not immediately clear how the attack would impact the election, though the issue of security has been thrust to the forefront of the campaign after the London Bridge and Manchester attacks.

The campaign was suspended for several days last month when a suicide bomber killed 22 people at a concert by U.S. pop singer Ariana Grande in Manchester.

Grande gave an emotional performance on Sunday at a benefit gig in the city for the victims of the attack, singing with a choir of local schoolchildren, including some who had been at her show.

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Before the London Bridge attack, May’s gamble on a June 8 snap election had been thrust into doubt after polls showed her Conservative Party’s lead had collapsed in recent weeks. [L8N1J007E]

While British pollsters all predict May will win the most seats in Thursday’s election, they have given an array of different numbers for how big her win will be, ranging from a landslide victory to a much more slender win without a majority.

Some polls indicate the election could be close, possibly throwing Britain into political deadlock just days before formal Brexit talks with the European Union are due to begin on June 19.

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UK SECURITY

May called the snap election in a bid to strengthen her hand in negotiations on Britain’s exit from the European Union, to win more time to deal with the impact of the divorce and to strengthen her grip on the Conservative Party.

If she fails to beat handsomely the 12-seat majority her predecessor David Cameron won in 2015, her electoral gamble will have failed and her authority will be undermined both inside the Conservative Party and at talks with 27 other EU leaders.

May said the series of attacks were not connected in terms of planning and execution, but were inspired by what she called a “single, evil ideology of Islamist extremism” that represented a perversion of Islam and of the truth.

But as a former interior minister, May’s record on security is also under scrutiny - police numbers were reduced every year under her watch and as Home Secretary she oversaw the domestic intelligence agency, MI5.

While she was interior minister, police numbers decreased every year. In March 2016 there were 124,066 police officers in England and Wales compared to 143,734 in March 2010.

Opposition Labour leader Jeremy Corbyn criticized May for cutting police numbers and repeated his pledge to recruit 10,000 new police officers, including armed officers.

“The mass murderers who brought terror to our streets in London and Manchester want our election to be halted. They want democracy halted,” Corbyn said in Carlisle, northern England.

“They want their violence to overwhelm our right to vote in a fair and peaceful election and to go about our lives freely.”

(Refiles to remove typo in paragraph 24 so that figure reads ... 143,734...instead of 1443,734)