Hi SM,
Depending on the consistency I want, I use either double cream (48% fat - this is what I normally use because I can control the consistency better 'cause it's thicker) or single cream (18% - less control over consistency 'cause it's runnier). BIRs probably most often use Ultra Heat Treated "UHT" (to preserve it) cream.
Mind you, I'm not overly health conscious! :
I'm sure a "fat-free" cream would work just as (well, nearly as) well....just less...um....creamy! Though I really can't see how you can take all the fat out of milk and cream and still call it milk and cream (water, more like!)!

;D
PS: If necessary, you can get away with a much shorter marination time SM (a couple of hours will do), or even don't mariante it at all! The depth of flavour and colour will obviously be less. Sometimes, when I'm in a hurry, I just fry the chicken in some tikka paste before adding it to the CTM sauce.