Thanks for the detailed suggestions @welshcatholic. Much appreciated!
I just followed what you suggested and copied the tracks for all three albums onto the desktop, deleted them from iTunes and then re-added them to the library.
And they all magically now appear in the same single Artist entry in the left-hand section! Amazing! Not sure what difference it makes removing the same tracks and re-opening them, but for now am just happy that it worked 🙂...
And BTW I know that additional spaces would cause a problem, but surely that wouldn't be the case with my example since I have selected ALL the tracks and entered the same data for all of them at the same time. Useful to mention it though of course.
Thanks again!
Note to Apple support team - can you explain why this is happening please?
cheers
Lawrence