I use "Musicians Insurance Services" based in Derbyshire 0845 345 7529 http://www.musiciansinsurance.co.uk
I have both my Equipment insurance and Public Liability through them, at what seems to be a fair premium for the cover you get.
Equipment is covered on an "all risks" basis in Britain and in the EU, with an option of overnight in an unattended vehicle, subject to certain conditions, (alarm, immobiliser etc).
Gear is also covered if left at a gig unattended (on stage, restaurant etc).
However, regardless of this, I never leave my Avalon anywhere!!
I have only ever had to make two claims, both accidental damage, but both were sorted, hassle free.
Hope this helps.