As it turned out, the chain was not the problem. It was the high pressure fuel pump. But ... the diesel-like clattering when the engine is cold gave all the warning signs so the local Peugeot mechanic recommended changing the whole lot anyway. Chain, tension bits, cogs, belts and guides. I knew it was coming so agreed to the work.
Peugeot's time scale for this job is 5.5 hours so you know how much that can be. I do advise anyone thinking about giving it to a workshop to make sure they know the engines and car. I have made this mistake before and wound up doing the job myself ( on a little 206+ car). Total cost without tax ..€2000.
Bye the way, I asked at BMW/Mini and they weren't interested in trying the job. Same engine different car and certainly a different clientel.
The motor sounds super now and I now have an acceleration unknown to me with this car.