I won a couple of years ago. I emailed to thank them, and they replied to me saying they receive many thousands of entries each week. I had a great time spending it in John Lewis! I thanked Priorslee at the time - it is so good of people to post competition details on here.
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a recent one
https://forums.moneysavingexpert.com/discussion/6207341/thank-you-priorslee-waitrose-crossword-win