You could try clamping the jump hose with a pair of vice grips (using a chunk of rubber or suitable cloth to protect the rubber hose). This should stop the flow to the slave cylinder and thus the pedal should be rock hard.
If the master is failing, the pedal will slowly go to the floor under foot pressure.
My suggestion would be to put a new Proline master cylinder in. The master can be taken out through the drivers wheel arch, if the pipes are disconnected on the master, unbolt the 6 bolts for the pedal assy, remove the LH splash shield and LH wheel assy and the whole master cylinder and pedal assy should come out through the wheel arch.
Some prefer this way, others prefer to take the whole LH wing/inner wing off.
Hope this helps.
Les Parker
Tech. Support and Parts Specialist
Rovers North Inc.