"Mainland Western Europe" (for the want of a better term) operates on Central European Time [CET], which is 1 hour ahead of British Standard Time [BST].
Both areas use daylight saving time in summer. HOWEVER, until recently, CET clocks changed on a different date from BST Clocks (or vice versa).
So, if you were in London, Paris was one hour ahead most of the year, but for two weeks it was two hours ahead, and for another two weeks, London & Paris were on the same time!
Great fun for Airline schedules!