Why does nobody ask an easy question ■■? 
My insurance is worked into a fleet deal and so saves me quite a lot of money.
We do not have GIT insurance the average cost of a load of concrete is about three hundred and fifty quid
Truck insurance policy reads something like RMC and all associated companies and all independant haulage contractors.
This way all of the o/d’s on for readymix benefit from the reduction in costs.
My premium last year was 2,300 fully comp with any employed driver covered, I could have got a further reduction of 500 quid if I had opted for cover to carry only RMC materials.
The best quote I could get independantly was 4,400 
cheers
STEVE.