Tim Farron told Scottish Liberal Democrat conference yesterday that Liberal Democrats would try to kill of the Tory tax credit cuts with a “fatal motion.” It’s the only one of the many resolutions opposing the measure that would actually stop it.

What’s interesting is that it’s clear that you can give the man a script, but you can’t make him stick to it. He actually said much more than was in the official version below. He added in a bit that said, directly, “Stuff the convention”, referring to the Salisbury Convention under which the Lords don’t defeat Government plans that were in their manifesto. Well, this wasn’t, Tim said, and Cameron explicitly denied he had plans to do it, so it was perfectly legitimate to take this action. Here’s the official version:

It’s the same with Dave, you can make a good speech pitching for the centre ground, but if your next act is to attack the hardest working, poorest people in Britain by slashing tax credits while giving away tax cuts to millionaires; you are in no ones centre ground, you are punishing people who are doing their best to get by. So I say “judge David Cameron not by what he says but what he does”.

In Scotland, almost 250,000 hard working families will lose an average of £1,000 a year that’s more than 300,000 children who are being made to bear the brunt of the Chancellor’s blind ideological obsession.

This is a policy that every independent organisation – from the Institute for Fiscal Studies to the Government’s own social security advisory panel – has said is ill-thought through, inexplicably punitive and deeply divisive.

In the House of Commons, MPs described the policy – and I quote – as a message ‘to the poorest and most vulnerable in our society that we do not care’ and called on the chancellor for, I quote, “something – anything – that might mitigate its harshest effects.” – and that’s just the Tory MPs.

So be in no doubt: this cruel, heartless, mean-spirited and misjudged policy is George Osborne’s Poll tax and we will fight it as we fought the Poll Tax – it will not stand – not on my watch.

That is why this week Liberal Democrat Peers have taken the lead and put down a fatal motion in the Lords to kill it.

David Cameron has reacted with fury. How dare we use the unelected Lords to defeat the government’s will! If only he’d had the chance to reform the House of Lords in the last parliament…. So, Dave, I will take great pleasure in hoisting you by your own petard.