'We shall never waver': MPs hold minute's silence for London victims
Theresa May on Thursday said Britain was "not afraid" as the country's parliament reopened a day after a deadly car and knife attack killed three people and injured 40 others
After a minute's silence at 9.33am, the British prime minister said: "We are not afraid and our resolve will never waver in the face of terrorism".
"At this time it is so important that we show that it is our values that will prevail, that the terrorists will not win, that we will go about our lives showing that unity of purpose and the values that we share as one nation," she told parliament.
May said the attacker, who has yet to be named, was known to British security services. She had earlier called the attack "sick and depraved".
In a statement made outside Scotland Yard on Thursday, the Metropolitan police's head of counter terrorism, Mark Rowley, said seven arrests had been made.
Hundreds of detectives worked through the night, carrying out searches at six addresses.
"The inquiries in Birmingham, London and other parts of the country are continuing," added Rowley.
"It is still our belief - which continues to be borne out by our investigation - that this attacker acted alone and was inspired by international terrorism.
Details began to emerge of the victims of Wednesday's attack on Westminster Bridge and near the Houses of Parliament, including the identity of a police officer stabbed to death.
Keith Palmer, a 48-year-old married father, was fatally wounded near Portcullis House before colleagues shot dead his attacker.
A woman in her mid-40s and a man in his mid-50s died in the ramming attack on Westminster Bridge.
According to a Spanish diplomatic source, the woman was a British citizen born in Spain, who taught Spanish in London.
Some 40 people were also wounded, including five South Korean tourists, two Romanians, a Portuguese man and three French schoolchildren.
The school pupils, aged 15 or 16, were on a school trip to London with fellow students from Brittany.
Britain's top counter-terror officer Mark Rowley has said that police suspect "Islamist-related terrorism". The attacker has not yet been named but Rowley said investigators believe they know his identity.
Palmer, the police officer, "was killed while bravely during his duty," London Mayor Sadiq Khan tweeted, "protecting our city and the heart of our democracy from those who want to destroy our way of life."
"He was someone who left for work today expecting to return home at the end of his shift - and he had every right to expect that would happen," Rowley said.
Parliament held a minute silence at 9.33am on Thursday – Palmer's shoulder number was 933.
Conservative MP for Braintree, James Cleverly, had served in the Royal Artillery with Palmer before the latter become a police officer.
He expressed his condolences, saying, "A lovely man, a friend. I'm heartbroken."
A woman was pulled alive, but with serious injuries, from the Thames, the Port of London Authority said. The circumstances of her fall into the river were unknown.
Tobias Ellwood, 50, a junior minister in the foreign office, was at the scene of the attack on Wednesday, and tried to resuscitate Palmer.
Speaking to Britain's Times newspaper on Thursday, he said: “What a mad world - tried to save officer but stabbed too many times.”
"I was on the scene and as soon as I realised what was going on I headed towards it," he said. "I tried to stem the flow of blood and give mouth-to-mouth while waiting for the medics to arrive but I think he had lost too much blood. He had multiple wounds, under the arm and in the back."