A man has described coming face to face with terrorist attacker Khalid Masood just hours ahead of his deadly attack in Westminster in which four people were killed.

Businessman Michael Petersen told reporters Masood had appeared “smiling, polite”, the night before the attack.

Mr Petersen was staying at a hotel in Brighton where Masood had also stayed the night before the attack, and he encountered the killer in reception.

“I noticed a very polite demeanour from the killer,” Mr Petersen told Sky News.

“There’s nothing in his conduct that would make me have suspicious thoughts towards him.”

Asked how the encounter with the terrorist has made him feel, Mr Petersen replied: “I have been thinking about that since.

“The shocking realisation that you can stand next to somebody that is totally, perfectly normal.

“Articulate, polite, presentable – and the guy is on his way to commit mass murder.

“That means it could potentially be anyone you're standing next to. That is quite a shocking realisation.”

Masood also reportedly told staff at the Preston Park Hotel in Brighton that London “wasn’t like what it used to be”.

A source told The Sun he chatted with staff at the hotel and told them he was “off to London today”.

Detectives traced him to the hotel thanks to a receipt left in the car he crashed into railings outside Parliament

Police have appealed to anyone who knew Masood to come forward with information.

He is believed to have operated under various aliases, and the Metropolitan Police have revealed he was born as Adrian Russell Ajao in Kent.

Masood killed three people with a hired car as he drove into pedestrians on Westminster bridge, before crashing the car and stabbing PC Keith Palmer outside Parliament.

Fifty people were injured in the attack and 31 required hospital treatment. Two people remain in a critical condition, one with life-threatening injuries.

Isis hailed Masood as a “soldier of the Islamic State” in a claim of responsibility issued the following day, although the extent of any involvement by the terrorist group remains unclear.

Scotland Yard's Deputy Commissioner Mark Rowley said officers were investigating whether Masood was radicalised by online jihadi propaganda or if he had been directed by the terrorist group.

“Our investigation focuses on understanding his motivation, his preparation and his associates,” he added.

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