Thanks RAJU,
I should have said that I've tried all of your suggestions before I posted here. This is what I have found -
All Lexmark proprietary drivers work fine for x86 and x64 but of course not WinRT, i.e., Lexmark Universal Driver.
The problem I have is with the Microsoft Class Driver.
I can appreciate that the Microsoft Class driver is more generic but if it installs one would expect it to work but it does not. Test printing completes but block characters are printed in place of any character.