Well, the reason for the alpha-numerics was because of the similar flight numbers that were causing even greater confusion.
I think the worst was BD1, BD51, BD251, BD581, and BD81 on the same freq/banded freq at the same time.
The alpha-numerics were trialled by CAA at Hurn and approved, and there have been tweaks since following user input!
So its really the best of a 'bad' job!