If they don't like the gift they'll very likely change it and not tell you about it, or wrap it back up and give it somebody else. It can be tricky buying gifts for your parents, as you may run out of ideas. Mums love flowers, even though they aren't a lasting gift. A bouquet of flowers is a gift from the heart. They also like things for the home or a good book.
Dads can be a bit tricky.
Why not buy him a tie or socks. Sock-Shop has some great designs at reasonable prices. Which brings me to Christmas lunch, and dinner, and snack, and cake. So what if you put on those extra kilos. You've got the rest of the year to lose them.