LONDON • British police warned yesterday that the country was facing an "increased level of terrorist activity", the day after a man carrying knives was arrested near Parliament and a woman was shot in a separate police raid.

Just weeks after the attack on the Houses of Parliament that left five people dead and scores injured, London is once again on high alert as Britain prepares for a snap election on June 8, reported Agence France-Presse.

"Yesterday was an extraordinary day in London," Deputy Assistant Commissioner Neil Basu, the senior national coordinator for counter- terrorism policing, said after confirming six arrests overnight. "I wanted to reassure the public that this increased level of terrorist activity is being matched by our action... We are making arrests on a near daily basis."

A 27-year-old man remains in custody after being arrested near Parliament on suspicion of terrorism offences and possession of knives, in what police confirmed had been an ongoing investigation. He has been named as Khalid Mohamed Omar Ali and is understood to be a British national from Tottenham, north London, who was born overseas, reported The Guardian.

Hours later in Harlesden, a suburb in north London, armed police launched an unrelated counter-terrorism operation that resulted in six arrests, five in the area and one in Kent, south-east England. The address had been under observation and the woman in her 20s who was shot was one of the subjects of the investigation, DAC Basu said, reported Reuters.

"The armed entry was necessary due to the nature of the intelligence we were dealing with and involved armed officers firing CS gas (tear-gas) into the address," he added.

"Due to these arrests that have been made yesterday, in both cases I believe we have contained the threats that they posed," he said.

The man arrested on Thursday, metres from Parliament and Prime Minister Theresa May's Downing Street residence, had reportedly been tracked by police and the domestic intelligence agency MI5.

A source familiar with the investigation said the suspect might have had contacts with militants outside Britain and travelled to meet them, but it was not believed he had been in contact with Islamic State in Iraq and Syria terrorists.

No one was injured in the incident and photographs showed three knives on the ground where he was arrested. DAC Basu said the man was being questioned and two properties were being searched in connection with the investigation.

During an election campaign speech on Thursday evening, Prime Minister May paid tribute to the police and security services, saying they were owed "a huge debt of gratitude", according to Agence France-Presse.