John Boeman is hitting on the right momma here I reckon.
Thing is, intermediary companies can get extra income from other firms offering bonus add-ons such as black cars and medical expenses for the missus, so can therefore offer insurance at a lower rate (sometimes) and with (obviously!) more benifits!
It is all a tricky game for the intermediary (I let the big-wigs down the booz..cough..the board-room work it all out) but they make wads and you can (sometimes) bet your bottom dollar they come up with a good deal for all!
VFE.