Russian aide row: advantage Moscow
It is highly unusual to expel a single foreign national for espionage activities. These incidents tend to involve the expulsion of a number of suspected agents all at the same time. The classic example is Operation Foot in 1971, when 105 Soviet diplomats were sent packing, or the departure of most of the KGB's London station in 1985 following the defection of the station chief, Oleg Gordievsky.
The reason for this approach is that if a security service is lucky enough to spot a suspected foreign agent (it doesn't happen very often), expelling that operative simply allows the enemy to send someone else instead and the hunt starts all over again. Instead, normal procedure is to put the agent under intense surveillance in order to learn as much as possible about operating procedures, communications routes and the presence of other agents. Then, once all the possible intelligence has been extracted from the operation, all the suspects can be rounded up and sent home together.
In the case of Katia Zatuliveter I suspect that MI5 has opted for expulsion because of the type of agent she appears to be. Given her age and background I very much doubt that she was sent to the west as a trained asset. Rather I suspect that she is someone who has developed access to useful information through the normal course of her career and that, perhaps during one of her trips back home, she is suspected of having been approached by the SVR, Russia's overseas intelligence service, and asked if she would "like to help".
This would be similar to the recent case of another Russian spy suspect, Anna Chapman, and in fact every intelligence service does a little of this - that is how the novelist David Cornwell (John Le Carré) got started in espionage, running simple errands in Berne for MI5 long before he was formally trained as an officer.
Zatuliveter never made any secret of her background, and she has clearly been under suspicion for some time because she has been interviewed repeatedly. Her internet and other activity will have been closely monitored by GCHQ, and it would have been able to pick up a trace of any communication with the SVR. That, together with complaints from MPs such as Chris Bryant, who chairs the Commons all-party Russia group, would have done the trick. There would have been little point in letting her run - if she was a spy, she was not a particularly important one.
There is one other interesting point to this case. I know that both MI5 and SIS (also known as MI6) are under a lot of pressure at the moment. The WikiLeaks documents revealed that SIS has admitted how it failed to make good use of the chance to penetrate the Russian intelligence services during the 1990s.
Meanwhile in the UK, the shift to counter-terrorism work by MI5 has meant that the Russians and Chinese are operating freely in London at levels equal to, if not above, those of the cold war. Curiously, in the case of Gareth Williams, the GCHQ officer who died in suspicious circumstances earlier this year, the most promising leads point to Russia and possible links to a UK intelligence operation. Given this climate, together with her unpopularity with certain government officials, it is hardly surprising that Zatuliveter is going home.
Yet in one important sense this case also represents a serious failure for the British intelligence services. They would have wanted to keep this expulsion very low key for fear of provoking retaliation by the Russian government. Both MI5 and SIS have extensive news management departments for this very purpose. However, this case is now front-page news, and there is a grave danger that the Russians might see the entire incident as an attack on their national honour.
The British intelligence presence in Russia has already been crippled by the expulsion of diplomats in 2006 following the assassination of Alexander Litvinenko. Another round of expulsions could prove to be devastating.