No, I don't think so. With some notable exceptions fares are priced in the currency of the city of origin. Even a complex itinerary involving multiple fare components will first be calculated in the currency of the country of origin.
But, if you pay on a CC from euroland the GBP amount would be converted to € by the CC company at whatever exchange rate they use. This is likely a better rate than the airline is going to give you. So you will pay in euros.