Nelson, 44, who comes from Belfast, was transferred from his isolation cell at the top security Crumlin Road prison, Belfast, before Christmas.
Nelson, a senior intelligence officer with the Ulster Defence Association, was the army's most senior Protestant agent in Ulster. A Northern Ireland Office spokeswoman refused to discuss individual prisoners but security sources confirmed that Nelson had been moved.
When Nelson was sentenced earlier this year, further charges that he was involved in the murders of two Catholics were withdrawn after the Northern Ireland Director of Public Prosecutions decided that the prosecutions were 'not in the public interest'.
Nelson allegedly had told his security service handlers of plans to murder two Catholics, but the security officers had not acted on this information. The decision to withdraw the further charges outraged Catholic churchmen and nationalist politicians, and infuriated the Irish Government.
Home Office officials negotiated Nelson's switch to another jail. Nelson flew out of Belfast accompanied by guards from the security services. He had waited almost a year for transfer arrangements to be completed.
Nelson has told friends that, with remission for good behaviour and the amount of time spent in custody before going to jail, he expects to be freed by 1996.
Friends of Nelson said he was 'extremely relieved' at the move. 'There were a number of threats on his life,' one friend said. 'The IRA and the loyalists want him dead and he was never allowed contact with anybody, certainly no other prisoners.'
Nelson's wife and children have been living in England for two years.
Nelson was sentenced after admitting a string of charges, including five of plotting to kill Catholics suspected of being members of the IRA.Reuse content