I had that a couple of years ago with Aviva...
I'm now with Chris Knott
http://www.chrisknott.co.ukBut have a go on an online comparison site and see what you get. CK will beat your other quote (usually) There's also a discount, if you are an SOC member, as they run the Saab Owners Club insurance scheme.
Greenlight, specialise in modified insurance.
But there are others that advertise in the SOC magazine. Peter Best, Adrian Flux, LV, etc.