The 70% figure comes from the basis that not all of the cable infrastructure will be upgraded this year, namely analogue only areas and very high cost upgrade areas. The 100% total they refer to is also a little misleading as it only accounts for the current digital network not analogue areas like parts of Southampton or Slough where decisions about their upgrade path are still being investigated.
I think even 70% seems to be quite an unrealistic target due to the amount of work that needs to be done but the company seems adamant this is possible! Seen as broadband is the companies new "hero" product then it would make sense to invest in infrastructure and get 50mb out as soon as possible!
VM are still remaining tight lipped over how the trial is progressing, vendors trialled and any sort of upgrade path they are following, the suspense is killing us who really want the service