Brillant!! Problem solved!!

Thank you Trevor and Mike. Your solution worked like magic.

The solution was actually staring me in the face because I always have the property box on view, docked to the side of the focus window.
I think I failed to recognise the solution myself, because in the property box, the up and down arrows in the spouse area actually move the tabs left or right rather than up or down.

Thanks again, both of you.

Regards,

John