Two times four is plenty, or how to calculate a journalist's IQ

Mark Lawson: Our prime ministers should be given an expiry date of eight years

stops on length of office better suit a presidential than a parliamentary system. While many countries with the latter system do have a constitutional definition of enough, term limits under such arrangements can increase the risk of coalition governments and prime ministers being chosen by MPs rather than the electorate - unless, as in the US, a separation between party and national leadership can be achieved.

And while term limits for leaders may be problematic (the second half of the second term inevitably becomes a waiting-room phase), an increasingly powerful moral and pragmatic argument for them exists.

There are days when the punditocracy makes you despair. Prime Ministers aren't chosen by the electorate - the electorate has bugger all to do with it. Prime Ministers are chosen by political parties, who sometimes even let their members have a say, albeit for completely different reasons - Labour needs to ask their members to try and counteract the votes of the various Unions in their bizarre electoral system[1], while the Tories don't want to ask their members in case they unearth another Ian Duncan Smith.

You can only have term-limits in a parliamentary system if you divorce the election of the Prime Minister from the parliamentary party system, i.e. implement some process where the Prime Minister is directly elected through a State-sanctioned system rather than appointed by a political party.

[1] Yes, I know there are historical reasons for doing things the way they do. This doesn't make it any less bizarre.