Possible Clues:

• Opposite number (colloq.)
• Research on a political rival, for short
• Whichever way you move, it's mate
• Colleague (colloq.)
• One's counterpart at work on the river
• Counterpart rings round very quietly
• Counterpart works back to back
• Research on a political rival, briefly
• Work, going forward and back, for counterpart
• ___ research (info on a political adversary)