Its an interesting idea, but when you start to think it through its full of holes? I mean, is £1million that much when you're 50 if you're not gonna get another penny til your 65? If you made it tax free on the payment and ensuing interest then possibly. But buying house, bills, car etc will eat a good chunk and how would you better yourself once you hit 50 if you can't get another job. You'll either get people hoarding, or as with the trend of the country, spending like tomorrow doens't exist.
Also, I wouldn't mind betting, give 50yr olds 1 million pounds and the majority would leave the UK. furthermore, treating alcohol and tobacco related incidents/illnesses I believe costs the NHS a fortune.
Threaten to shut down 'major polluters' will cause industry to leave UK, therefore reducing jobs/tax. I read somewhere PCs are a bigger contributer than the airlines for CO2 emissions, so you give 1million to 50yr olds they are going to buy PCs and sit round watching p0rn all day, more emissions issues (though possibly good news for tissue companies).
So I vote, nice idea at first, but no.