Angus McCullough QC is acting as special advocate for Katia Zatuliveter, the Russian parliamentary assistant to the MP Mr Hancock, against whom a deportation order has been made in relation to alleged spying activity.

The judge, Mr Justice Mitting, has ruled that Sir Stephen Lander, Former Director of MI5 can remain on the panel which decides whether the MP’s former aide accused of spying should be deported from the UK.

Those representing Russian Katia Zatuliveter, 26, argued that the former head of MI5 could not be seen to be impartial. But the judge decided that Sir Stephen’s expertise was needed by the Special Immigration Appeals Commission.

Government lawyers say Miss Zatuliveter is an agent for the Russian Intelligence Service, and should be deported from the UK on the grounds of national security.

Sir Stephen, who was MI5 director general from 1996 to 2002 during a 27-year career at the security service, will be in a three-member panel deciding the deportation case.

At a hearing in London it was argued that Sir Stephen was a “cheerleader” for MI5 who had given media interviews about Russian intelligence.

But Mr Justice Mitting, who will chair the Special Immigration Appeals Commission panel, said: “In my judgement an informed and fair-minded observer would recognise that the intention of Parliament [is] that we should equip ourselves where possible with sufficient expertise to deal with the very difficult and very important questions we have to determine.”.