Thanks Kaas. I have worked it out. I have a skydome in the model and although it does not interrupt the view in sketchup it hides it when exporting. Switched it off and all is well. Simple, but took me a few hours to work it out.... First time I have used a skydome in a long while.

OK - I sorted it out. Right click and render. I didn't realise you have to do this sometimes when Auto render is selected.

Thanks. Yes I have always found Layout very frustrating and it is only because I have bought a new computer with a lot more RAM that I am even considering it. I think I am getting there with a system that works for me - a few more weeks and hopefully I will have it cracked. Thanks for your reply.