Tony Curzon Price (London oD): Warning! New constitutions are made in crisis, to solve a crisis that the previous order has failed at. Graham Allen MP says (entry below) "Why should a Prime Minister want this [a written constitution]? Because, we the people want it because it is our country not his and the next Prime Minister needs to be a democrat." I would remind him of the birth of France's Fifth Republic (see useful link here). The highly parliamentarian Fourth Republic (itself born out of Vichy) failed to solve the Algerian problem: war, terrorism, mutiny in the Organisation Armee Secrete, bombs in Paris... The leaders of the Fourth republic pleaded for de Gaulle to come out of his memoir-writing exile and save France. De Gaulle agreed, on condition he could change the constitution.
The constitution of the Fifth reflects the dilemma of that moment: de Gaulle needed centralising powers to solve the immediate crisis in Algeria as well as the issue that has brought down every Fourth republic government: the separation of church and state schools. The resulting constitution is two-headed and weird: there is no clarity about whether the President or the Prime Minister rules. The pro-Parliamentarians wanted the second; the Gaullist camp wanted the first. From 1958 to 1968, de Gaulle used referendums to try to make the constitution more presidential (most notably the direct election of the president in 1962). His sparring partner, the SFIO's Francois Mitterand, wanted decentralisation. It was not until 1986 that the true ambiguity of the constitution emerged with "alternance" and President and Prime Minister from different political camps.
Back to Graham Allen: "Why should a Prime Minister want this?" Because there is a crisis that nothing else will solve. If you want a good constitution, you have to hope for the right crisis.