A man injured in the London 7/7 bombings fears he might be deported from the UK.
Professor John Tulloch, who lives in the Vale of Glamorgan, south Wales, once held a British passport and has spent most of his life living and working in Britain.
But now semi-retired, the India born academic whose parents were British, said he has been told he is no longer entitled to remain in the UK indefinitely.
Border Agency officials have questioned his entitlement to a UK passport.
But Prof Tulloch, who until recently discovered he had a lesser form of British nationality known as "British subject without citizenship", has described the situation as bizarre.
"My wife has a British passport, my sons both have British passports, my brother - who was born in India - has a full British passport but not me," he added.
"My family goes back in Britain to (the year) 1200 or something. It's been traced, so what do you do?"
Prof Tulloch was one of hundreds injured in the 7/7 blasts in 2005 when four suicide bombers attacked central London, killing 52 people.
Shards of shrapnel were embedded in his face and he has suffered symptoms of post-traumatic stress disorder.
He told the inquest into the 7/7 deaths that he was partially shielded from the blast by the luggage at his feet.
Prof Tulloch said the uncertainty over remaining in the UK was worse for him than 7/7 because had been "lucky" on that day.
He had survived then managed to go on a "journey" which saw him write two books related to his experiences.
But now he says he is struggling to stay in the country because of circumstances outside his control many years ago.
Prof Tulloch went to school in Bournemouth before attending Cambridge University and later gaining further qualifications at Sussex University.
He then applied for academic jobs at universities in Britain, but landed a job at the University of New South Wales in Sydney, Australia.
"That's why fortunately I went to Australia, never thinking there was any issue of my losing my British residence," he explained "The issue that caused this is because I took out Australian citizenship in 1983."
He said that unknown to him, the Australian citizenship cancelled his British nationality and his right to live in Britain.
And when he tried to renew his passport around 20 years ago it was confiscated - much to his bemusement.
Later using his Australian passport with a work permit, Prof Tulloch held senior roles at Brunel University in London and the journalism school at Cardiff University, among others.
But said he had been told by a senior immigration officer at Heathrow Airport he would not be able to stay in the country indefinitely.
A UK Border Agency spokesperson said: "If you are a British subject otherwise than by connection with the Republic of Ireland or a British protected person you will lose that status on acquiring any other nationality or citizenship.
"It is the responsibility of an individual to check that they will not lose a previously acquired nationality or citizenship on acquiring an additional one."