A man armed with a knife was arrested after threatening to kill Croydon Central MP Gavin Barwell in his constituency office.

Police have advised the Conservative to keep the doors to his Shirley office locked at all times following the "disturbing" incident on Friday afternoon.

The constituent threatened Mr Barwell and two of his staff and used "racially offensive language" after making "serious allegations" about the Government at a surgery appointment, the MP said. 

Office staff called police to the office in Wickham Road at about 2.10pm on Friday.

Officers arrested a 24-year-old man on suspicion of racially aggravated harrassment and possession of a bladed weapon.

Mr Barwell said the man, who was detained under the Mental Heath Act, was found to have a knife in his bag.

He told the Croydon Guardian: "An individual made a surgery appointment with me but it soon became apparent that there was no way I was going to be able to help him with the thing he was raising.

“He was making some very serious allegations [about the Government] but had absolutely no evidence to back them up.

“I gave him several opportunities to produce evidence but he didn’t so I told him I was going to have to ask him to leave.

“He refused to leave so I told him if he really wasn’t prepared to leave then we had no choice but to call the police and to ask them to remove him.

“He became increasingly agitated, began kicking the furniture around, used racially offensive language and then threatened to attack me and threated to kill me, it was quite disturbing.

“When the police arrested him they searched his bag and discovered he had a knife on him, but at no point were we aware of that.”

He added: "It wasn’t as scary as it sounds, to be honest I just thought ‘this is somebody that isn’t very well’ and he was clearly agitated so we were just trying to calm him down.

“It was only right towards the end when the police arrived that he threatened to attack me and he threatened to kill me, that’s when I got concerned.

“It wasn’t a pleasant experience certainly."

Mr Barwell emailed constituents on Tuesday to inform them his office would be locked "for the moment" on the advice of police and that constituents should call his office to make an appointment if they wish to see him.

He added: "I have reluctantly taken this advice. I have always wanted to be as accessible as possible, but clearly my first duty is to ensure the safety of the people I employ.

"I hope you will understand why for the meantime I need to take these precautions."

A Metropolitan Police spokeswoman said officers were "investigating an allegation of racial aggravated harassment".

The arrested man has been bailed until late July.