In UK pounds only, but there will be an ATM wherever you land in France or Spain to get your Euros. You could get Euros at the airport change places but the rate will be bad to worse than at home as Can$-£-Euro will cost you.
I was just trying to save time, by getting money in london. You see when i land in biarritz i will only have one hour to get to the train station in Bayonne to catch the last train out, just wanting to save time. perhaps i'll get enough euros here until ST.jPDP.