Three people are now known to have been killed during a terrorist attack on the Houses of Parliament in London.

An attacker, who also died during the incident, drove a vehicle along the pavement of Westminster Bridge before crashing into gates surrounding Westminster Palace.

As many as 40 others are thought to have been injured, with seven in a serious condition.

The assailant was shot and killed by armed police after stabbing an officer to death.

The dead officer was named as PC Keith Palmer, 48.

The attacker has not been named.

However Mark Rowley, head of counter-terrorism at the Metropolitan Police, said the forced thought they knew who he was.

He added the Met believed he was inspired by Islamist-related terrorism, but gave no further details.

Seven arrests have been made this morning in raids following the attack, police have said.

Rowley paid tribute to PC Palmer, saying: “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.”

Aysha Frade, 43, and US tourist Kurt Cochran have been named as the two people killed on Westminster Bridge.

Cochran’s wife, Melissa, is among the injured and is being treated in hospital.

One woman was also rescued after falling into the River Thames as the attacker drove on the pavement of Westminster Bridge.