I found the issue with one tyre, a needle or something in the tyre. It could not be felt until I turned the tyre inside out. Only found it because a second tube got an obvious puncher, the first tube still seems to have no hole on a casual inspection, a water test would find it. The issue with the other wheel though is still a mystery, but it's replaced now. I think I just had two separate issues on consecutive days leaving me confused somehow trying to link them.

Glad you found the issue. Like I had mentioned a fine piece of wire is hard to locate but will cause a slow leak. Andy