£17.99 has always been the normal price, you had been on some sort of a deal which has now ended. Check out what value packs you can now have
http://www.home.ntl.com/icat/valuepacks
On another note, NTL are in the process of upgrading all 1mbit users to 2mbit. You might have been upgraded and you can check this from the speed test on this site.