David Cameron's team is always on the lookout for clever ways to wrong-foot Gordon Brown at Prime Minister's Questions.
Instead of spotlighting the latest lacklustre economic figures or the war in Afghanistan, they decided he should raise an issue preoccupying the shadow Education Secretary Michael Gove.
Shortly before the weekly meeting just between the leaders, Mr Gove talked Mr Cameron through the controversy over the alleged links between two schools and the hardline Islamist group Hizb ut-Tahrir.
During the meeting in the Tory leader's private room, Mr Gove told him that the organisation that ran the schools had secured £113,000 of public money, some of it from the Pathfinder scheme designed to fight violent extremism.
In the Commons, Mr Cameron briefly succeeded in making the Prime Minister, who was expecting to defend his economic record, look uncomfortable.
But the money at the centre of the dispute had come from a separate Pathfinder scheme designed to pay for nursery places.
The blunder by the Tory team was said to have been made by a researcher who put together a briefing paper ahead of Prime Minister's Questions.
But it also created deep embarrassment for Mr Gove, who is one of the Tory leader's most trusted advisers and confidants. He has been highlighting the case of the two schools for nearly a month; the rapid revelation of such a basic mistake leaves him with egg on his face.
Senior Tory sources conceded last night that it had not been a "perfect operation", but they insisted Mr Cameron had no regrets raising the issue.
They argued that the crucial point – the links between the school and Hizb ut-Tahrir and its receipt of public money – had been demonstrated. One said: "We are on the right side of the argument."