Updated and resolved.
Thanks to Matt from Pimoroni for his help in replacing the unit the next day for me.
The new unit still wouldn't work so I searched further and found the following link:
http://arduinotronics.blogspot.co.uk/2014/10/fingerprint-scanning-with-arduino.html
This states that the voltage divider on the TX and RX is NOT required. I tried this and it worked perfectly. This is despite all the test sketches and instructables pages saying it is required.
Really happy now,
Thanks again
Kev