Election UK - Clegg Unique Opportunity

I voted for the Liberal Democrats because they were against the invasion of Iraq and they are in favour of proportional representation. I believe that despite the disappointing election result for the Lib Dems - which is hardly surprising since most electors are afraid that under the undemocratic 'first past the post' system in the UK at present their votes will be wasted. This is because Britain sometimes resembles an elective dictatorship. Clegg uniquely has an opportunity to change this. He must demand, as a quid pro quo of supporting (hopefully Labour under a new leader) that there is an immediate change in the constitution to introduce PR (hopefully STV version). If this requires a referendum, then so be it.