The family of the police officer who was killed in the Westminster terror attack have thanked those who helped him in his final moments, saying: "There was nothing more you could have done."

PC Keith Palmer’s relatives said they were “overwhelmed” by the support they had received.

"We want to thank everyone who has reached out to us over the past few days for their kindness and generosity,” they said in a statement released by Scotland Yard.

“The police have been a constant, unwavering support at this very difficult time. It has made us realise what a caring, strong and supportive family Keith was part of during his career with the police,” they said. “We can't thank them enough.”

They added: "We would also like to express our gratitude to the people who were with Keith in his last moments and who were working that day. There was nothing more you could have done.

"You did your best and we are just grateful he was not alone. We care about him being remembered for his selfless bravery and loving nature.”

In pictures: Westminster attack Show all 9 1 /9 In pictures: Westminster attack In pictures: Westminster attack An air ambulance lands after gunfire sounds were heard close to the Palace of Westminster in London PA wire In pictures: Westminster attack MPs wait until the situation is under control in Westminster. 'The alleged assailant was shot by armed police,' David Lidington, leader of the House of Commons, told the house. BBC News In pictures: Westminster attack Crowds gather in Westminster after shooting incident, which police are treating as terror attack BBC News In pictures: Westminster attack Police were also called to an incident on Westminster Bridge nearby AP In pictures: Westminster attack Early reports indicate the car, which mounted the pavement on Westminster Bridge and mowed into around a dozen people, was the same vehicle which then rammed into the railings of the Palace of Westminster, just around the corner Reuters In pictures: Westminster attack Security sources described the suspected assailant as a middle-aged Asian man, who is understood to have left the car before attacking a police officer with a seven-to-eight inch knife PA wire In pictures: Westminster attack Police have asked people to avoid the immediate area to allow emergency services to deal with the ongoing incident AP In pictures: Westminster attack One woman has died and a number of others, including the police officer, have been hurt, according to a junior doctor at St Thomas' Hospital Reuters In pictures: Westminster attack At least three gun shots were heard by those inside Westminster, and proceedings in the House of Commons have been suspended AP

PC Palmer was stabbed to death by Khalid Masood, who ploughed a car into pedestrians on Westminster Bridge before crashing his car into railings and then running into the grounds of Parliament, armed with a knife.

Police then shot the 52-year-old who was born as Adrian Elms in Kent.

Detectives from the Metropolitan Police's Counter Terrorism Command have now confirmed that the terrorist attack carried out over within 82 seconds.

Deputy Assistant Commissioner Neil Basu, who is the Senior National Coordinator for UK Counter Terrorism Policing, said: "Our investigation continues at pace. I am grateful for the public support so far, but I am asking for more help.

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"If you knew Khalid Masood and had spoken to him in the months, weeks or days leading up to this attack please come forward.

"We still believe that Masood acted alone on the day and there is no information or intelligence to suggest there are further attacks planned.

He added: "Even if he acted alone in the preparation we need to establish with absolute clarity why he did these unspeakable acts to bring reassurance to Londoners, and to provide answers and closure for the families of those killed and the victims and survivors of this atrocity.