Sacheverell de Houghton, 56, was already serving 10 years for kidnapping and blackmailing another man who had escaped, William Boyce QC, for the prosecution, said.
Mr de Houghton targeted the millionaire known only as G, planning to take pounds 20m in ransom, Mr Boyce said. He recruited another prisoner, Everton Morrison, to act on his release as his lieutenant and put together an abduction team.
Mr de Houghton and Mr Morrison, 30, both deny conspiracy to murder and conspiracy to kidnap between January 1993 and February 1996. The former also denies soliciting murder and incitement to kidnap.
Mr Boyce said "De Houghton wanted to take G somewhere remote in the Scottish Hebrides or southern England ... This time the plan was to kill him so there could be no witnesses."
From his cells in various prisons over a three-year period, Mr de Houghton negotiated the purchase of a castle on the Isle of Coll in the Hebrides and an estate in Cornwall and set up bank accounts in Cornwall and Denmark, it was alleged.
Mr Boyce said the plot involved bait for the millionaire: in 1991 Mr de Houghton had told his victim he was a dealer in Russian icons; G was interested in furniture. "The ruse was to say De Houghton had a very valuable item of furniture. He wrote to G indicating he had furniture for sale. G was hooked."
Mr Morrison was visiting Mr de Houghton regularly in prison, the court was told. Mr de Houghton was dissatisfied with the first team Mr Morrison had recruited and a second team was found. But among them was an undercover detective.
By February 1996, there were fears that Mr de Houghton was suspicious of the undercover officer and the police decided to make arrests. When interviewed by police Mr de Houghton allegedly said he was acting on the orders of another prisoner whom he feared.
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