@NewJudge
//Those wishing to elect a government rather than an MP are seeking ways of abolishing the constituency link and they would do well to remember that.//
Yes, hence the warning set out in Mosaic's post. Wouldn't it be ironic if the LibDem desperation to get "more of a voice in Parliament" (not even a hope of actual unbridled power) opened the gateway to something extreme, like fascism, sweeping in on a tide of popularity, at first and then intimidation tactics once it reaches a critical mass? That is the chief fear but it it would be undemocratic to 'lock out' specific political themes.
All the same, we need to bear in mind that introduction of PR could inspire the spawning of new parties but, as with consumer choice, we'll end up with a perma-resident market leader and a series of 'niche' parties, all making a noise, trying to get their voice heard, to no end whenever the division bell rings.