Some of the Yonex racquets I've bought recently have serial numbers just above the handle. They start UK followed by five numbers, and I did buy them in London. The dealer told me they are a security measure, but I'm not sure how they can ensure that your racquet is genuine. Surely, counterfeiters can also fake numbers? Is there any way to confirm your racquet's serial number to make sure you have a real Yonex?
You can possibly contact Yonex to find out if your racket is real or not. The "UK" basically states that this racket has been made or purchased in United Kingdom. I have a racket from TH which is from Thailand. Or you should look at your racket and see if it's real or not.