First, thanks to all those who replied to my original post. The good news is that the problem was indeed a split hose, which has now been replaced, and we're back on the road. The slave cylinder was replaced a couple of years ago when the gearbox had to come out due to a failed speedometer drive. Clutch was also replaced at this time - round about 120K miles from memory. The master cylinder died around a year ago, and was replaced, so I guess it remains to be seen whether either of these components survives any muck which the disintegrating hose may have introduced. The car has been dealer serviced from new, and the original pipe did appear to have a braided exterior. The replacement pipe is smooth. So...fingers crossed.
Thanks again folks...