If this law means that "legal" downloads became as cheap as getting the CD/DVD off ebay (or the local charity shop, etc) then I'm all for it. Ooh look, a pink elephant with wings!
Anyhoo... I actually think that by blocking off the 'illegal' routes there will be no incentive to reduce prices in the UK for legal downloads; quite the opposite. So while the rest of the world (except China) will download and enjoy British films and music for free, the British public won't be able to afford them.
I propose that in return for kowtowing to the copyright holders and blocking (allegedly) infringing sites, parliament should legislate for a maximum price chargeable on content downloaded to British IP addresses - say £2 per GByte. I'm sure we could rush that amendment through parliament before the election, along with everything else.