Thanks for that. Yes it is Marchant Dice Ltd.
The diameter of the screw is 12mm.
I am not sure if the assembly will allow the removal of the drive nut without the lead screw being in place, but I will try and assemble it without the lead screw and see if I have a problem with the carriage as well. I can only access it at weekends and then I don't have access to the internet so my progress might be slow.
Any idea of how to tackle / align the other two axis?
Thanks again.