Liberal Democrat Mike Hancock is challenging the security services to produce evidence against Katia Zatuliveter, 25, who faces deportation after being arrested late last week.
She came to the UK three years ago to study for a masters degree at Bradford University before starting work a few months later as a researcher in Mr Hancock's parliamentary office in the House of Commons.
The MP is a member of the defence select committee but denied his researcher would have been privy to any secret information that was not available to the public.
Describing Ms Zatuliveter as "bright and intelligent", Mr Hancock said yesterday: "I have no reason to believe she did anything 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 per cent - 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."
Ms Zatuliveter is appealing against the deportation order, which came after Home Secretary Theresa May was briefed by MI5 about the assistant's alleged connection to Russia's foreign intelligence service.
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.
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Mr Hancock said he had spoken to his aide yesterday morning and she told him she had not seen any evidence against her.
He said she had been interviewed by the security services in August after she was stopped as she returned to the UK from holiday. She had a tier-one visa, reserved for highly skilled workers.
"Nobody has shown me any evidence to support the view that she is any way a threat to the UK," he said. "If she was a threat, when they stopped her in August, they could have removed her then."
The researcher was arrested at 7am last Thursday. "She was asked to pack a bag, get ready and 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," the MP said.
Mr Hancock is MP for Ports-mouth South, a city which has a large naval base. As a defence select committee member, he has insisted his work is not "top secret", although he has asked for information on the location of nuclear submarines and has probably asked more defence questions than any other MP.There is no suggestion Mr Hancock has acted improperly.
He added: "As far as I am concerned, there was nothing she was doing for me that was sensitive. Defence select committee papers have been leaked to newspapers before now and I have never read anything in a defence select committee paper or report which was worth someone believing they couldn't get it from another source."
Ms Zatuliveter, a Russian who originates from Dagestan, was forced to flee her home as a child in the mid-1990s during the Chechnyan conflict.
Her work included hosting constituents during visits to the Houses of Parliament, writing speeches and working on early-day motions, the MP said. She was currently researching a report about obesity.
The level of Russian espionage is believed to be approaching the levels of the late 1980s during the Cold War. It was thrust into the spotlight in July when 28-year-old Anna Chapman was among a ten-strong spy ring thrown out of the US.
The group were later handed a medal by Russian president Dmitry Medvedev for espionage work in the West.
Work and Pensions Secretary Iain Duncan Smith said yesterday the Zatuliveter case was a cause for concern. "I would say normally this would be a joke, but actually after what's been going on with some of the spies that Russia seems to have put in all sorts of places, you have to take it quite seriously," he said.
Shadow foreign secretary Yvette Cooper said vetting procedures for those applying to work in the Commons might have to be re-examined.
"It is important to make sure those (procedures] are strong enough and secure enough," she said. "If there do turn out to have been breaches in security, then the wider security in parliament would need to be looked at."
Kim Howells, the former Labour MP who chaired the Commons intelligence and security committee, said it was the job of spies to infiltrate policy-making circles and report back to their handlers in Moscow details such as public opinion.
He said the Russians would have been very interested in finding out details about the large naval base in Mr Hancock's constituency, and added 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 said.
Former Russian spy Oleg Gordievsky, who defected to the UK in 1985, said of the FSB (formerly the KGB): "Russians are spying just as much as before, only now it's easier because Russians believe that the western public is very, very easy.
"All bits of military information are of great importance to the FSB. (Zatuliveter] would have very easy access to it and lots of other information at the MoD.They use that information to make foreign policy decisions."
A Home Office spokesman said only: "We do not routinely comment on individual cases."