sqad
There have been 21 cases of people being deprived of their citizenship since 2002 when Blair seized these powers in emergency legislation after 9/11.
here is some background on each case.
http://www.thebureauinvestigates.com/2013/02/26/medieval-exile-the-21-britons-stripped-of-their-citizenship/
There are two cases that could be the one referred to in the OP.
E2
Afghan-born. Deprived March 2012. Siac appeal rejected August 2012
Afghan-born E2 is described in Siac papers as a 36-year-old male who became a British citizen in 2009 and ran a business in London. While visiting his family in Pakistan, the Home Secretary deprived him of his nationality before he could return to the UK. In court papers E2 says he only learned that he had lost his citizenship on May 25 2012, when a British embassy official informed him at Dubai airport as he tried to fly home. His appeal was rejected following a partially secret Siac hearing.
Y1
Afghan-born. Deprived July 2011. Appeal dismissed May 2012. Proceedings are ongoing.
An Afghan asylum seeker, Y1 became a British citizen in 2004, married and had a son here. In 2010 he left London for Kabul, accompanied by his second wife, also British. According to court papers Y1 was arrested by UK forces in Afghanistan in summer 2011, after visiting Pakistan’s tribal areas. He was stripped of his citizenship on terrorism grounds on the same day as his release without charge in July 2011. Y1 challenged the order, arguing it would make him stateless. However Siac rejected the appeal.
In both cases, if he is a terrorist, we should interrogate him and he should go to prison if found guilty.
I think the problem arrises because there is no evidence that would stand up in court. They are charged and convicted by the Home Secretary without their knowledge. They are not allowed to know what the charges are or what the evidence is. They cannot defend themselves or question evidence or the conclusion by some unknown official. That is not British Justice.