Pre-pay handset commerical deals in the UK?

Saw this on MoMoLondon and wondered what the answer was:

Does anyone know the approximate commercials around pre-pay retailer sales in the UK
market?

I’m not looking for detail, simply something on the lines of:
“retailer gets around x % of handset sale cost” etc.

Anyone know?

Many thanks

Paul

I’d like to know too.