Possible Clues:

• Coal-mine representative?
• Person acting on behalf of another
• One performing duties when superior is absent
• Sheriff's surrogate
• Assistant
• The next in command, replaces boss when necessary
• Mistyped the letter U in 'substitute'
• Assistant with power to act in the absence of superior
• You'd turn up around the T.D. placed in here
• Legislator from European Parliament in service