After the past month of messing about and the Smart garage not having a clue, they have now decided that it is not possible to turn the air bag off using the car seat. It only works for the first stage car seat, and not the next stage up. Dh has told them this is not acceptable for us and we believe there recommendation is not safe enough.
So it is cancelled
However, for just £200 more I am now going to, hopefully, get a FourFour Passion - the four seater Smart car. Not convertible though, but still pretty cool, and definitely more economical than my Beetle. Dh is going to speak to them and see which ones they have in stock. I am happy to compromise on colours
Don't have to spend £190 on their car seat either now. Can just get a normal one. No isofix sadly (I don't think anyway - best check!) but PILs have just got DD a Britax Hiliner seat, reduced to £40 on Toys R Us which did really well in the Which report, so may get that one.
So, fingers crossed this one goes well.