Thanks for all the advice guys. I finally got some time to spend on the bike this afternoon - I've done a bit of fiddling and the QR's a bit better, not perfect in my opinion though. It's easier to release the mechanism rather than close it.
After riding it a bit, it remained firmly in position even though the roads around here aren;t known for their perfect surfaces. Here's a photo of it as far closed as it goes. Please bear in mind that it hits a "stop" rather than "it's so stiff I can't close it any further".
is it on a frame-brazed hanger or is it on a separate hanger plate? .
It is indeed on a frame-brazed hanger. Thanks for your kind offer Polar Bear
Eck's probably right - I'm just paranoid (but he would say that wouldn't he - he's out to get me you see)
RJMcB