To
finish off...
Have
just got off the phone with a company called Bits 'N' PC's (www.bnpcs.com) which is run by Mike Huggins
and which happens to be a (possibly *THE* given the amount of parts they
seem
to have off the shelf) main dealer for HP spare parts ... they do online
ordering and there is a link to HPs "Parts Browser" which meant that I
could
visually locate the assembly that I needed.
Turns out that £42 + VAT will source me the entire pump assembly
complete with ink cartridge receiver, motor, control PCB, sensors
etc.