Labour leader Ed Miliband's Prime Minister's Questions briefing notes were left in a toilet in Commons, the BBC reports.
According to political correspondent Norman Smith, they contained pre-prepared lines to rebuff David Cameron over a row about Labour's candidate choice for Falkirk involving the Unite union.
The notes were also said to contain pre-emptive responses to any criticisms of Labour MP Tom Watson, including "I'll take Tom Watson over Andy Coulson any day".
Mr Smith said a Labour source admitted that Mr Miliband's parliamentary aide left the notes behind, quoting them saying "he left the chamber in a hurry!".
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What separates us from the terrorists is that we air our grievances with non-violent debate though our democratic structures and processes.