In case this is helpful to anyone we have just sorted out our site insurance. We got quotes from (with the actual insurance company in brackets):
Buildstore (Catlin Insurance company)
Buildzone (EC Insurance)
Protek (QBE Europe)
Self Build Insurance (Zurich)
Self Build Insurance (Zurich) were almost 30% cheaper than the other 3 so definitely worth a call.
We have gone for 24 months as it seems that lots of people on here end up having to renew half way through and premiums can be hiked at that point.
Hope we don't need to use it. And hope we get it finished within 24 months.....we are starting tomorrow with knocking down our garage and will attempt to finally locate our water supply (where Thames Water, a diviner and alot of hand digging has failed hopefully a digger bucket will do the job ) .