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!".
More top news
The poor response to the devastating fire at Grenfell Tower was "ultimately a failure of values", the Archbishop of Canterbury has said.
The president of the European Council, Donald Tusk, said he still hopes that the UK might change its mind over Brexit and decide to stay.
A blind veteran has launched a heartbreaking appeal for the return of his war medals, after they went missing while returning from Normandy.