| Short answer no - but, I have used the BMW isofix seat which is good a) becuse it's really firmly fixed into the car and b) More importantly it is dead easy and quick to secure your kiddie becuse there is only one strap, and there is not much room for an adult and a flailing child in the back of a mini when it's peeing down with rain on a busy road.
However, it's expensive about £280 I think (will last until they are about 7 though. The Mini dealer tried to convince me to buy the Mini branded version which is identical (even has the BMW badge!!) and guess what the mini one is £30 more expensive.
We do have a Maxi Cosi seat for our other car - I think it is a simialar design to the mamas & papas one. I reckon it would be pretty difficult to get the thing in and secured just because there is so littelt room to enable you to tighten the mini belts to the seat itself.
Hope this is of some use. | 
