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A British MP whose parliamentary aide was arrested over claims she is a Russian spy has challenged the security services to "prove their point now".

said Katia Zatuliveter, 25, had nothing to hide, he backed her 100%, and would appeal.

She now faces deportation proceedings after she was taken into custody on the orders of MI5,

The Home Office said it did not routinely comment on individual cases, nor would it confirm deportation moves.

Mr Hancock, MP for Portsmouth South, told Sky News: "I have no reason to believe she did any thing but act honourably during the time she was working for me.

"She is determined to fight her corner and she genuinely believes, and I back her 100%, that she has nothing to hide and has done nothing wrong.

"If she has, the (security) services are right. But they need to prove their point now."

A security source is said to have told the Sunday Times that Ms Zatuliveter's presence was not "conducive to national security", and the intention was to "show her the door".

It is believed to be the first time since the end of the Cold War that someone working in Parliament has been accused of spying for the Russians, suggests the Sunday Times.

Mr Hancock told the ´óÏó´«Ã½ he was standing by Ms Zatuliveter, who he said had been arrested at 0700 GMT on Thursday and was subject to a deportation order.

"She was taken away and held in a detention centre in London, and then transferred to another detention centre where she is putting her appeal together," he said.

Mr Hancock, who sits on the House of Commons Defence Select Committee, said Miss Zatuliveter was not involved in any sensitive work.

"I have never read anything in a defence select committee paper or report which was worth anyone believing they had something they could not get from another source," he said.

´óÏó´«Ã½ security correspondent Frank Gardner said Russian intelligence agencies had a "very low threshold" for information and they would frequently "try to acquire by covert means what is out there on the internet or in open publications".

"It doesn't surprise me at all if this is true but it does seem very strange that she was picked up some time ago and that she was vetted," he said.

Ms Zatuliveter was first stopped in the summer and had been interviewed by police four or five times since.

Our correspondent said it was possible the UK security forces knew about her activities and had been "playing her".

"To me, it strikes of a little bit of incompetence that they would vet this woman and allow her to be in a position of some sensitivity," he said.

The level of Russian espionage was back up to where it was in the late 80s, he said, and there were up to 35 Russian intelligence officers working covertly in the UK who then employ others.

He added that the Russian government is thought to have an "extensive shopping list of information" it is trying to acquire through covert means - on the aerospace industry, defence and information technology, as well as politics and diplomacy.

Ms Zatuliveter started working as an assistant to Mr Hancock in 2008. She had previously been an intern at the House of Commons and had worked in Europe.

Work and Pensions Secretary Iain Duncan Smith told Sky News the allegations were a cause for concern and had to be taken "quite seriously", while shadow foreign secretary Yvette Cooper said vetting procedures for those applying to work in the Commons might have to be re-examined.

And Kim Howells, the former Labour MP who headed the Commons Intelligence and Security Committee, said there needed to be much sharper vetting of parliamentary assistants.

"I think the Foreign Office and intelligence services are acutely aware of this threat and I think they are going to be looking at making more funding available for the security services to tackle this kind of threat. I hope they are anyway," he told Radio 4's The World this Weekend.

The latest allegations come after 10 Russian agents, including Anna Chapman who had dual Russian-UK citizenship, were expelled from the US in July.

Author Chapman Pincher says spy games have increased because the Russian PM Vladimir Putin is determined to restore his country's status in the world.

"They were a superpower until the collapse of the Soviet Union, and he wants to get back to that position, so it's business as usual," he said.

"Espionage here is much easier now because most of MI5's resources have to be devoted to the terrorist threat."