Former British soldier Simon Mann has expressed regret for his part in a foiled plot to overthrow the leader of Equatorial Guinea. Mann, 57, is expected back in the UK later after being pardoned and released from jail in the West African state. He had been sentenced to 34 years, but was pardoned on Tuesday along with four South Africans. Before leaving, Mann said: I regret what happened in 2004. It was wrong and I'm happy that we did not succeed." Speaking in the country's capital, Malabo, Mann thanked the authorities: "I am very grateful for this pardon. "I am extremely grateful not only for my pardon but for the way in which I've been treated from the moment I arrived here in Equatorial Guinea in 2008." He is believed to have been reunited with his sister and brother. Mann had admitted plotting to oust Equatorial Guinea's president, but had said he was only "a pawn" in the plot. Sources in Scotland Yard's Counter Terrorism Command have confirmed to BBC News that officers want to talk to Mann. A Metropolitan Police spokesman said: "We can confirm we are investigating whether any offences may have been committed in this country. "We are aware of developments but are not prepared to discuss them further. We are liaising with the Crown Prosecution Service. Inquiries continue. The Counter Terrorism Command are investigating." In March 2004, police in Zimbabwe impounded a plane from South Africa. They arrested Mann and 63 others on board amid suspicions they were mercenaries intent on toppling President Teodoro Obiang Nguema. The Briton served four years in a Zimbabwean jail before being extradited to Equatorial Guinea where he was tried and convicted. Mann was sentenced to 34 years despite pleas from his lawyer that he had been "not a co-author" of the coup plot but "an accomplice". 'Profoundly grateful' On Tuesday, an adviser to President Obiang, Miguel Mifuno, said that Mann had been released on humanitarian grounds related to his health - he had a hernia operation last year. Mr Mifuno said: "Simon Mann conducted himself in exemplary fashion during his trial and his incarceration in Equatorial Guinea. "He has had some health problems, and was operated on. He is now in good health but the president thinks he should now be allowed to live in peace with his family." He also told BBC News that the releases had been timed to coincide with a visit to Equatorial Guinea by South African President Jacob Zuma. One of the freed South Africans, Nick du Toit, told the South African Press Association that the prisoners had been told President Zuma and his government had been involved in the negotiations for their release. A spokesman for Mr Zuma, Vincent Magwenya, said: "It's possible that the government of Equatorial Guinea had believed it needed to release them on the eve of President Zuma's visit. "But that was not a condition from our side, to say they must do that on the eve of the visit. We do believe it satisfies the legal provisions of Equatorial Guinea." Sources close to Mann have told the BBC's security correspondent Frank Gardner that his release came as a huge shock to him. They say talks have been going on for a year, but Mann knew nothing about the pardon until last week and his wife Amanda was kept in the dark until Monday evening in case it fell through. In a statement earlier, his family said they were "absolutely delighted" at his release and were "profoundly grateful" to President Obiang. Suspended sentence Equatorial Guinea's ambassador to the UK Agustin Nze Nfumu told the BBC World Service that Mann's brother and sister had travelled to the capital to greet him ahead of his return to the UK. Mann, who used to live in Beaulieu, in Hampshire, has a son, born during his time in prison, he has never seen. Mann had implicated London-based Lebanese millionaire Ely Calil and Sir Mark Thatcher, son of former UK Prime Minister Margaret Thatcher, in the coup. Sir Mark, who now lives in southern Spain, was fined and received a suspended sentence in South Africa in 2005 for unknowingly helping to finance the plot. He said he was "delighted" that Mann would be reunited with his family. Mr Calil also said he was "thrilled" at the news. Equatorial Guinea, an oil-rich former Spanish colony, has been ruled by President Obiang since he seized power from his uncle in 1979. Source: BBC