Here are some pics. The paint inside the tube has worn away which could make a difference. My calipers tell me that the cup is around 30.1 mm diameter. I have ordered a new headset from wiggle and will look into adding some varnish.

I plan to get the frame shot blasted (£10 by local company) and then I'm going to respray myself.

Thanks for the helpful comments - a very friendly forum...

Martyn