In London and brought my car from OZ

[mad.matt]

Welcome!

As has been mentioned, I believe the handbrake has to work independently of hydraulic action to pass an MOT.
Being an emergency brake, it has to be usable in case of line rupture/fluid loss.
If it's plumbed in to standard rear calipers, see if you can find yourself an OEM handbrake and cable set and offset your hydraulic to keep its functionality.

This might sort out your dash "issue" but I just had a phone holder with GPS speedometer app, worked very well and you could set up speed warnings etc if you had a heavy right foot.