And the Labour leader's day got worse when a briefing paper containing all his killer responses turned up in a toilet in the House of Commons.
The three-page note, reportedly found in the gents toilets near the Commons Division Lobby, indicates the Labour leader was clearly expecting Cameron to go on the offensive and includes a list of suggested responses.
Under the heading "Falkirk" it says: "Let's have a debate about ethics. This is Prime Minister who had dinners for donors in Downing Street, gave tax cuts to his Christmas card list and brought Andy Coulson into the heart of Downing Street."
This was the precise comeback Miliband turned to when Cameron did indeed raise the Unite boss.
A further suggested response is: "Let's make the contrast. We're taking action. A year ago he had the scandal of dinners for donors in Downing Street, commissioned an inquiry but since then total silence."
Under the heading "Unite Buying Influence", the proposed riposte is: "This is the man who buys donations with a millionaires tax cut and holds dinners for donors in Downing Street."