Sad as I am, I've quickly calculated what the outcomes might look like if we had a compromise PR system. This system is based on needing to meet a threshold or win seats for inclusion in parliament.
Unsurprisingly, the Lib Dems are the main beneficiaries but the figures I'd calculated suggest that the Greens should have a much larger voice based only on those willing to "waste" their votes.
The SNP and Plaid also get additional seats, but there are no seats (yet) for UKIP, the BNP or Ulster Unionists. For the UU, this is only because they'd not won a seat when I calculated this.
If we had 650 seats, then:
Conservatives 252
Labour 204
Lib Dem 160
SNP 12
Greens 7
DUP 4
SF 4
Plaid Cymru 4
SDLP 3
Clearly, the vote distribution would be different under any pr-ish method. However, it's worth noting for PR opponents that most system don't guarantee representation for the likes of the BNP. Indeed, it's probably as easy for the BNP to focus attention on a single constituency (like Barking) and fight on "local" issues and win a seat than get a large proportion across the country.
(For those sad enough to care, I've used a vote threshold of 5% and the Sainte Lague method.)