I did have some doubts to begin with. The rev counter was twitching in an unusual manner. That alone made me consider an electrical problem elsewhere.
I was taken down the timing chain route, by a previous experience on a Zafira that ran the same. & new chain sorted that.
After the first post I looked harder at the cams & chain & the tensioner protrusion extended to about 15mm after the inlet cam was turned so that the slack was on the tensioner side. The slack was so bad that the cams would turn independently by approximately one tooth.
I was a little curious that it hadn't set a cam sensor code though.