Yes, it is common for British people to say "Happy Christmas" instead of "Merry Christmas." In the UK, "Christmas" is often pronounced as "Cristmas" instead of "Chrismas" like in the US, and the term "Happy Christmas" is a more traditional and formal way of wishing someone a happy holiday season. The phrase "Merry Christmas" is also used in the UK, but "Happy Christmas" is considered more formal and polite, and it is often used in more traditional or formal settings.