You can have PR or election promises, but not both

Oh, the injustice of it. The great thing about being a Lib-Dem candidate is that you can promise any damn thing you fancy in your election leaflet in the sure and certain knowledge that you will never be in power, writes Peter Rhodes.

And then, hell's teeth, you find yourself in coalition with the Tories and that line about you never agreeing to raise tuition fees comes back to haunt you.

As Vince Cable reminds us, the road to Whitehall is "covered in the skidmarks of political parties changing direction."

The university-fees row is also a reminder that proportional representation (PR) often delivers coalition government, which inevitably produces U-turns and compromise.

No politician who believes in PR has the right to make any election promises - and don't believe any beaming candidate who tells you otherwise.