Well I just tried to get the 10Mbit upgrade (Sammy) and was told I would be charged £50!!!
After reading the comments here I might have another go at CS and see if they would be polite enough to install a free SACM (I have all three packages) - wish me luck!
p.s. What would would happen if I downgraded to 2Mbit for a month then requested the 'new' 10Mbit service in January? Would NTL have to supply me with a new modem?