MPs have questioned parliamentary security following revelations that a suspected Russian spy worked undetected in the House of Commons.
Liberal Democrat MP Mike Hancock has stood by his assistant Katia Zatuliveter insisting she had "nothing to hide" as she faced deportation for allegedly being a spy.
Mr Hancock challenged the security services to produce evidence against Ms Zatuliveter, who was arrested on Thursday morning and is currently being held at an immigration detention centre.
The 25-year-old, who came to the UK three years ago to study a masters degree at Bradford University, held a House of Commons pass and underwent security vetting before taking up her position as a full-time assistant two-and-a-half years ago. She worked previously for the MP as an intern.
MPs have insisted that a review of Commons security must take place if breeches in the system are discovered.
Ms Zatuliveter is appealing against the deportation order, which came after the Home Secretary Theresa May was briefed by MI5 about her alleged connection to Russia's foreign intelligence service, the SVR, The Sunday Times reported.
Yesterday, it emerged 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.
It is not known what prompted Ms Zatuliveter's arrest but a source told The Sunday Times she was no longer welcome in the UK.
The source said: "Her presence here is not considered to be conducive to national security.
"There was unhappiness about what she could have access to. The intention is to show her the door."
Mr Hancock, a member of the Defence Select Committee, also represents Portsmouth South, where the Ministry of Defence has significant naval interests.
If it is confirmed Ms Zatuliveter is a Russian spy and she is deported, it will be the first case since the Cold War of a Russian agent being removed from the Houses of Parliament.
Describing Ms Zatuliveter as "bright and intelligent", Mr Hancock told Sky News: "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%, 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."
He said the first he knew about Ms Zatuliveter's arrest was on Thursday lunchtime when he received a telephone call to say she had been detained.
Mr Hancock added he hoped she would be at work as he was unable to make it to the House of Commons because he was snowed in.
In an interview with the BBC, 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, which are reserved for highly skilled workers.
Mr Hancock said: "Nobody has shown me any evidence to support the view that she is in any way a threat to the United Kingdom.
"I am surprised. I haven't seen anything, and they (the security services) haven't contacted me recently and they didn't give me any warning she was going to be detained. She has a perfect right to appeal and I am sure she is confident of winning the appeal."
Meanwhile, MPs said there must be a security review of Parliament if the system was breached.
Shadow foreign secretary Yvette Cooper told BBC1's Andrew Marr Show said: "There are parliamentary security checks on anyone who applies for a House of Commons pass, anybody who is going to work in the House of Commons. Of course it is important to make sure that these are strong enough and secure enough.
"Depending on what happens in this individual case, if there do turn out to be problems and breaches of security here, then obviously the wider security in Parliament would need to be looked at, and I am sure the Speaker would take that very seriously."
Work and Pensions Secretary Iain Duncan Smith told Sky News: "I have never seen or met her and the trouble is 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 into all sorts of places, you have to take it quite seriously really I suppose."
Labour backbencher Paul Flynn defended Ms Zatuliveter, describing her as "an affable, serious, highly intelligent woman" and suggesting the spying allegations were implausible.
"Her command of English is superb and she is comfortably at home in the United Kingdom. Her background is international," Mr Flynn wrote on his blog.
"A great deal of nonsense has been written about her and her family. Her father is not a billionaire Oligarch. Katia's parents are of modest means.
"All the conversations I have had with her have been about parliamentary business and gossip - not what I would expect from a Mata Hari. That name is a reminder of a woman who was falsely accused.
"Katia is evidence of the remarkable collapse of the barriers between East and West since 1990 when she was five years old.
"Was she trained as a Russian Spy in school? As she has spent most of her life outside of Russia, the accusations against her are not immediately plausible."
A spokesman for the Russian embassy said it had not been notified by the British authorities about Ms Zatuliveter's detention.
Ms Zatuliveter herself had also not asked for assistance from diplomats, he added.
"We have not received any request from any interested parties," the spokesman said.
Asked about suggestions that Ms Zatuliveter was being expelled in revenge for Russia's victory in the bid to host the 2018 World Cup, a Downing Street spokeswoman said: "That's a bit far-fetched."Reuse content