Vernon Bogdanor's important new book, The New British Constitution, points out that there has been no shortage of constitutional innovation in the past 12 years – from devolution to funding political parties. But this shows signs of running out of steam. The constitutional renewal bill, now becalmed in parliament, is a ragbag of issues.

We need to address electoral reform and reform of parliament. Two principles come to mind – the separation of powers and parliamentary sovereignty. The first has been adopted by many countries but the separation of executive, legislature and judiciary has been espoused most zealously by the US. The striking thing about the UK is how little we have adopted this principle. Before reform in 2005 we tolerated a lord chancellor who sought to be a minister, a judge and Speaker of the House of Lords.

But the key area where the separation of powers is not observed is in the overlap of executive and legislature. The party that can command a majority in the House of Commons forms the government andrecruits about 100 MPs to staff it. This was for many years seen as a strength of the British constitution, what Walter Bagehot identified as the “efficient secret” or “the close union, the nearly complete fusion, of the executive and legislative powers”, with cabinet being responsible to parliament.