Hi Mark

I think everything's been said about what might happen to red diesel next year. It's a sobering thought that you might be paying Ł7/mile if you dare to open the throttles.
A note of caution, though, if I may. Nothing could be more different than a Camargue 55 and an Oceanis 50, except the price. If you fancy sailing, great, but you'll need an army of like-minded friends available when you are, to do winchgrinding and spinnaker snuffing or whatever it is you have to do to make headway (actually starting the engine is the most reliable). I would not want to discourage you from whatever takes your fancy but bear in mind buying a boat just while waiting for things to pan out might be very expensive. Aside from the depreciation, selling a boat can take several months and generally costs 6% agent's commission.
I would definitely try sailing/driving both your chosen boats before taking your purchase decision. These are very big boats for a first time purchase. Also, think about marina charges and maintenance which will add substantially to the fuel bill.
Good luck with whatever you decide.