Liverpool Software Gazette published an article about XTAL Basic. I have made this available in the Magazines section of this web site.
The program was later updated to version 2.2 as far as I know. I have been told that this BASIC, although it looks a lot like M****soft, was actually written completely independently. It certainly runs very nicely (or at least my copy did about 15 years ago - I havn't tried it since...).
The really clever thing about Xtal BASIC was the ability for the user to add their own key words to the language. The associated command routines were stored in a separate area of the memory from the BASIC code and could be saved and loaded with the interpreter. This meant that a version could be customised for a particular type of job.
I sometimes wish that this language was still around... :-)