I am returning to the UK for a couple of years after 11 years living in France. Who are the best insurers, ideally those with whom I can get an online quote?

Try an online search through one of the search facilities such as www.moneysupermarket.com which can be found here

Direct Line are worth a try also here but guess you will end up ringing the cheaper companies to see if they will offer any sort of No Claims Bonus based on your driving history in France

Unfortunately I don't think you'll have much luck online. As the last 11 years of driving is based in France, most insurers will recognise/accept that, however, it's unlikely their online sites will be able to cope with anything other than bog standard risk - a bit like modifications, most insurers are ok with it but just not online.