The ongoing fuss about "Purdah" in the run up to the referendum on EU membership seems to be completely missing the point. Purdah is borrowed from the Persian word for a curtain or veil, and in this context describes the period before an election or referendum where government can not make announcements or introduce new policies which could influence the outcome of the election. Cameron has pointedly refused to have this period of purdah before the EU referendum against opposition from secessionists including his own backbenchers.
Cameron's stubborn refusal to adhere to this convention at first appears to be simply his own Europhile leanings wishing to use taxpayers' money for pro EU political ends. This in itself would be bad enough, but I suspect there's something more to it. After all even in the Scottish referendum, which Cameron appeared to be in favour of winning, the convention was observed.
The difficulty with purdah in the EU referendum is that it would imply that the European Commission was prohibited by British law from campaigning for an In vote during the referendum, and this is something that the British government does not have the power to do. Enforcing purdah would mean that the British government would be obliged to prosecute European Union officials for using public funds for campaigning. Since British law is, and even after "successful" negotiations still will be, subordinate to European law this would be a nonsense. It would be like a local council prosecuting the British government, when the end game will be that the sovereign power will overrule local officials.
This is not some wild conspiracy theory. The European Commission intervened in the Irish referendum on the Lisbon Treaty, using tax payers money to secure a Yes vote. This was considered unlawful at the time by some, however it seems that nothing came of any legal challenge.
The popular assumption seems to be that Cameron is suspending purdah because he wants to use the British state to promote the In vote is actually understating the amount of power we have already lost to the European Union. He is avoiding this because he knows full well that the European Commission will simply pay no attention to purdah, putting him in the embarrassing position of having to either enter a legal battle with the Commission or publically accept, at the very worst time politically, that EU officials are above British law.