Possible Clues:

• One sent back down the river?
• Vote in European swindle for one who's served his time
• About ninety, one exercising, one having done a stretch?
• Prior prisoner, for short
• One's got out of jail as a political defector?
• Old time-server is political turncoat perhaps
• Halfway house resident
• Former jailbird
• One's rehabilitated a defector to Labour?
• Reformed criminal