Mr Hughes had appealed for witnesses to come forward following a murder in his London constituency. But one "witness" - a Turkish illegal immigrant, accompanied by a relative - used his "evidence" as a way of bargaining for leave to remain in Britain.
"Mr Simon Hughes, God bless him, must have been putty in the hands of these two," Jonathan Goldberg, QC, defending, said. "The whole situation must have been like manna from heaven.
"That nice, proper, affable Englishman had wanted to do the best for his constituents, the police and the public to encourage witnesses to come forward in this horrible murder. He was conned."
The claims were made as Mr Goldberg made his final speech in the trial of five youths accused of murdering 17-year-old Jamie Robe, who was beaten to death in Rotherhithe, south-east London, early on 7 August 1997. The accused - Aaron Cole, 19, James Pearce, 19, David Huggins, 18, Steven Plank, 18, all of Rotherhithe, and a 16-year-old youth who cannot be named for legal reasons - deny the allegation.
Mr Goldberg said that among the witnesses who came to court to give evidence for the prosecution during the trial were a former illegal immigrant from Turkey and his nephew. He said the man had earlier equipped himself with a forged Dutch passport to present to the Home Office in order to get employment cards.
"Suddenly comes an opportunity - laced with a daily newspaper's offer of a handsome reward - to cure the illegality," he said.
"It can be cured overnight and Simon Hughes says he will use all his best efforts."
He said Mr Hughes acted after the Home Office immigration service had written to police in April saying they would not grant permanent immigration status to the witnesses. Mr Hughes had two meetings with the Home Office minister Mike O'Brien in August and September, and had persuaded the minister to overrule his own civil servants, he said.
"This was a successful con, a brilliant con. They have haggled for their evidence. They went to see Simon Hughes in February and he made them all these liberal promises. The question is whether you will also be conned or have the scales removed from your eyes at what has gone on," Mr Goldberg told the jury.
Earlier in the trial he had accused the immigrant's nephew of selling his evidence so his uncle could remain in the UK. The 30-year-old man, who gave evidence from behind screens because he fears reprisals, denied the claim.
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