I have Geico on my Smart, and the most competetive rate to boot! Britboy, I assume your not in the UK, so what state are you in, maybe that's the reason? Can you get an online quote from Geico, they do have the smart listed.
I tried Progressive, State farm, and Liberty Mutual (paired with Merc finance, and Smart for the highest quote yet - 1473/6)....Geico - Good record, 3 vehicles and $243/6months - 50/100/50