Theresa May says 'enough is enough' after London attacks

Prime Minister Theresa May has vowed to strengthen counter terrorism efforts after the UK's third deadly terror attack in as many months claimed the lives of seven people.

A downcast May addressed media outside her Downing Street office on Monday after three men ploughed into pedestrians on the London Bridge and stabbed others as they walked through Borough Market on Saturday night.

May condemned the "evil ideology of Islamist extremism" after the second terror attack on UK soil in the past two weeks.

The Manchester bombing a week earlier which killed 22 people including an eight-year-old girl.

"We believe we are experiencing a new trend in the threat we face as terrorism breeds terrorism," May said.

"Perpetrators are inspired to attack not only on the basis of carefully constructed plots ... and not even as lone attackers radicalised online but by copying one another and often using the crudest of means of attack."

May said the series of attacks were not connected in terms of planning and execution but were inspired by "Islamist extremism" which represented a perversion of Islam and of the truth.

She said this ideology had to be confronted both abroad and at home.

"It is time to say enough is enough," she said during a televised statement.

"We cannot and must not pretend things can continue as they are," May said, calling for a strengthened counter-terrorism strategy that could include longer jail sentences for some offences and new cyberspace regulations.

The murderous rampage comes only days before Britain's general election.

Campaigning had been suspended for four days after the Manchester Arena bombing, however May said the newest attack will not hold up the election.

"Violence can never be allowed to disrupt the democratic process."

Twelve people have now been arrested in connection with Saturday night’s deadly attack.