Have you read #9 of
http://www.plus.net/support/faq/broa...sage_faq.shtml ?
The Plusnet idea may be OK if you want to stay up until 1:00 am to start your downloads and make sure you stop them by 8:00 am . If you don't and you are heavily downloading then your peak time usage may soon hit the cap. Your peak time usage (17 hours a day) will be restricted and have to be watched.
Who knows how soon Plusnet will have to change their usage model, especially if all the NTL heavy users move over to them?