So, after the Tories attempted to divert attention away from the Ashcroft affair with a crude assault on the trade union movement, today they find themselves back under the spotlight.

Papers leaked to the BBC show that William Hague was consistently kept informed about the negotiations of Ashcroft's tax status and that he was "satisfied" with the final outcome in July 2000. All of which seems rather at odds with the shadow foreign secretary's earlier claim that he only discovered Ashcroft's non-dom tax status a "few months" ago.

Hague's rather lame defence on the Today programme this morning was that he was not a "tax accountant", and that as leader of the opposition he had "a thousand and one problems at a time".

It may well be that, rather than engaging in an elaborate cover-up, Hague simply didn't realise that Ashcroft had wriggled out of paying his fair share (again). But neither option is particularly palatable. If he did know, then he's too wicked to hold office, and if he didn't know then he's too stupid.

Chris Huhne got it right this morning when he argued: "William Hague is not fit for any role in government, let alone that of foreign secretary."

Hague's importance to David Cameron cannot be overstated. The Tory leader's decision to appoint him as his de facto deputy in 2009 was a crucial move, designed to reassure the right of the party. He is one of the five shadow cabinet ministers who will lead the Tories' election campaign.

Hague must now show the sort of dignity that has been so lacking throughout this affair and resign his post.

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