I suspect that the patent if it has been granted is almost certainly invalid on the grounds of prior art. Possibly also on the grounds of obviousness.

I worked in the UK Patent Office many years ago and although things have changed greatly since then, in my day the only search requirement was on UK patents, so the examiner may not have turned up a prior patent. However, it is still possible to challenge a Patent on the grounds that the alleged invention is already known and has been previously published.

This device is certainly not new, I would also say it is pretty obvious. I came up with the same idea about 20 years ago and made one. Though I have not seen it published elsewhere, that it has been does not surprise me. I used mine for a number of years before I finally threw it away because it was falling to bits.

If you really feel like it, call his bluff.