Pricing oil in euros makes economic sense to Europeans, because it eliminates the currency (dollar) risk. Norway is part of the European free trade zone, and has therefore most of its imports and exports other than oil priced in euros. http://www.energybulletin.net/13081.html
The same holds true for the bilateral trade between Germany and Russia http://www.themoscowtimes.com/stories/2003/10/09/047.html
La grande nation, the French also would prefer to buy oil in their own currency. http://www.finanznachrichten.de/nachrichten-2005-04/artikel-1892089.asp - 18k
So when Britain becomes net oil importer in the near future the switch from dollars to euros just might be a logical next step.
But the British Pound is traded separate from the Euro as well...