This possibly shows how difficult things would be under PR. There would be months of wrangling and shady deal-making behind the scenes given the nature of UK politics ('we'll support your policy if.......' etc) to either form an effective coalition. Cameron would be PM (as the tories would have...
It's not a 'fact' though is it.....not everyone who voted Tory did so because of the Labour/SNP 'threat'. The vast majority of the 36% have probably always voted Tory. It may be though that the threat convinced enough others to vote Tory to affect the final result.