Mike,
I've just ordered one of these.
http://www.amazon.co.uk/dp/B007G5CJ1K/?tag=unique09f-21
It's an adapter that will enable you to plug your original apple charger into the 2 pin euro socket which is fed from the invertor (so will work off the leisure battery). The one I've ordered is expensive but it is supposedly a genuine Apple accessory and since work has just bought me a shiny new macbook pro I'd better not risk blowing it up with a dodgy adapter.
There are much cheaper (approx £5) ones available on eBay. The risk should be minimal as I'm pretty sure the adapter is passive.
I should be getting it mid-week so I'll confirm whether it does the job.
Dave