Thanks Shalini,
I uninstalled the driver and re-installed from the link you provided. This did not change anything.
As I have said, I do not get any error messages when printing, and the printer prints completely fine for everything, except when I am printing an A1 size PDF, reduced to fit A3 paper, then it still prints, it just doesn't print all the lines etc.
If I print the same reduced size drawing from my colleague's Apple computer it prints perfectly. I have been told that this is because Apple have a generic postscript driver "built in" whereas PC's don't. Is there something within my system, rather than the printer driver, that I can change?
cheers