Yes my gear lever does have a sliding sleeve to select reverse. However after Christmas I intend to get under the car and have a good look at the box and linkages to check condition and type.
This whole process has intrigued me over what I thought was a standard component - the MT75 box. I assumed with minor variations all such coded gearboxes were the same. No - there are 2 and 4 wheel drive versions, different gear ratios depending on the car, different gear lever arrangements and from your comment even different reverse selection methods. I am pleased to say though that I have learned a great deal.
Thanks again for your advice.