The Freeview EPG lineup is being rejigged in September to reorganize the channels to better grouping of like services. General channels will be from 1 to 99, the HD channels will move from 50 to 101, Kids TV will be 121-130 and there will be a new Freeview HD information page on channel 100.
There is a statement on the DTT Multiplex Operators web site detailing the channel changes, I am not sure if Windows Media Center will need re-tuning manually of it it will pick up the changes automatically.
The changes will happen September 19th
Thanks to Jason for the tip