Possible Clues:

• Uninvited guest
• Unwelcome guest
• Uninvited party guest
• Charge rates, otherwise someone will attend uninvited
• Uninvited attendee
• Keep in Conservative with less sense who shouldn't be in party?
• One getting in without an invitation
• A detective stopping poor Shergar's unwelcome visitor
• One culpable by self-admission
• Charge rates, otherwise he will attend uninvited