Well thank you Chris - that has got me 95% of the way there. Its a curious story . . . 5% to go !

1. When I press CTRL C in the souice workbook, the cells are successfully pasted to the clipboard.
2. In the destination workbook, the cells are visible in the clipboard, but CTRL V does nothing.
3. Clicking on the item in the clipboard successfully pastes to the destination workbook
4. And . . . subsequently, CTRL V pastes it again

It is as through CTRL V is only being activated after the first paste has been made.

So I thought it might be something that has reassigned CTRL V, but it isn't . . . I put the Paste command on to the Quick Access Toolbar and it is greyed out until I have used the clipboard dialog to paste something, then the QAT button becomes activated and I can paste it again ! If I put something new on the clipboard the paste function is once again disabled.

So, you've given me a workaround - thank you for that - and now I am even more bemused what's going on