The NUT has already fallen foul of it. The advert it submitted to Teachers was rudely blue-pencilled by no less a figure than Labour's general secretary, Margaret McDonald.
The crime? A reference to its campaign for "a properly-recognised profession free of payment by results". The NUT was told that this was "implicit criticism of Labour's policies ... not acceptable in our own magazine".
NUT general secretary Doug McAvoy is unimpressed but he promises not to censor David Blunkett the next time he gets free space in the union's house mag.