A book of condolence has opened at Sheffield Town Hall following the terror attack in London yesterday.
It has emerged this morning that the man who carried out the attack in Westminster, central London, was known to MI5.
The British citizen had been investigated some years ago over violent extremism, said Prime Minister Theresa May.
Delivering a defiant message to a packed House of Commons, Mrs May said: "We will never waver in the face of terrorism."
In addition to the attacker, three others died yesterday.
Paying tribute to PC Keith Palmer, who was stabbed as he tried to prevent the attacker storming the Houses of Parliament, Mrs May said: "He was every inch a hero and his actions will never be forgotten."
A man and woman died after they were mown down on Westminster Bridge.
Forty people were hurt in the attack with 29 treated in hospital, where seven remain in a critical condition this morning.
The injured included 12 Britons, three French children, two Romanians, four South Koreans, two Greeks, and one each from Germany, Poland, Ireland, China, Italy and the United States. Three police officers were also hurt, two of them seriously.