Elections 26 October 2015 What is a statutory instrument, and why has it put the government on course for defeat in the Lords? The measure has put the Conservatives on course for a defeat in the Lords this afternoon. Photo: Getty Images Sign UpGet the New Statesman\'s Morning Call email. Sign-up The government could face an embarrassing defeat in the House of Lords over cuts to tax credits later today, likely triggering a war of words between peers and the Conservative government about the constitution and the Salisbury-Addison convention. What’s going on? It all comes down to a legislative manoeuvre called a “statutory instrument” – effectively a device that allows the government to move legislation through parliament more quickly than passing a new Act. If, for example, the government wanted to amend a law on cellphones to include, say, tablet computers – it might opt to do so with a statutory instrument, avoiding the months of legislative back-and-forth that a new Act would entail. The government has chosen, rather than a full-blooded Bill, to amend aspects of previous legislation on tax credits. This made the passage through the Commons easier and quicker – avoiding more scrutiny and perhaps helping to avoid further outbreaks of nerves on the part of Conservative backbenchers. But that means that the House of Lords is also able to vote on the measure – as Britain’s unelected second chamber isn’t allowed to vote down finance bills, but can vote on the statutory instrument. In fact, government defeats on statutory instruments, once rare – prior to 1997, the Lords defeated a statutory instrument just once, in 1968 – have become increasingly common since Tony Blair partially reformed the Upper House, removing the bulk of its hereditary peers. Since then, the Lords has voted down statutory instruments in 2000 (twice), 2007 and 2012. But what about the Salisbury-Addison convention, the agreement between Lord Salisbury and Lord Addison. Salisbury led the Conservative peers in 1945, when the Labour government had a landslide majority in the Commons but just 16 members of the House of Lords. He did a deal with his Labour counterpart, Lord Addison, that the Lords would pass the Labour party’s manifesto commitments, no questions asked. Labour and Liberal Democrat peers believe that the guarantees made by various Conservative ministers during the election campaign that tax credits would escape the axe mean that the measure is very far from a manifesto commitment. Labour notes, too, that their amendment to the statutory instrument doesn’t reject the cuts entirely – but asks the government to come up with measures to soften the blow, well in keeping – they argue – with the role of the Lords as a revising chamber. The Liberal Democrats, however, are going further. Their amendment would vote down the bill entirely – a measure that appears unlikely to draw support from Conservative backbench peers or the “crossbenchers” – peers who do not take the whip from any political party. As I've written before, the defeat may pave the way for the government to create a Conservative majority in the Upper House through creating a large number of Tory peers. Theoretically, of course, there's nothing that would prevent them from doing so. But their central argument - that members of the House of Lords are behaving unconstitutionally - doesn't quite wash. › How and why central Paris shut down its last major refugee camp Stephen Bush is political editor of the New Statesman. His daily briefing, Morning Call, provides a quick and essential guide to domestic and global politics. He also co-hosts the New Statesman podcast. Subscribe For more great writing from our award-winning journalists subscribe for just £1 per month!