Strange Power Loss during Warming up Period Cooper S R56

Hi All,
Sorry my first post is a 'please help' post!

My wife has a 2007 Cooper S. It has the JCW kit but I am not sure it actually is, based on the air filter it has.
Anyway here is my problem.....
1. Start the car from cold, no problems drives perfectly.
2. If you keep driving without stopping, for example if you got straight onto a dual carriage way then no problems.
3. If I stop at a junction when the coolant temp is over about 30 Deg C but under 104-105 Deg C, it then loose a lot of power when I set of again.
4. This loss of power will resolve itself when the engine is fully up to temp, say 104 Deg C, but ONLY if I come to a stop again, then set off.

The loss of power appears to be from lack of boost. From my code reader it shows 122 kpa WOT @ 2k rpm when loss of power occurs. When it is driving fine that same test shows 175-180kpa.

This happens every time I drive.

I am very familiar with turbo charged engines, but can't figure this one out!

Any Ideas? Thanks in advance