Just to give an update, I removed the air filter box from the car to gain access to the clutch hose. The price of £108 or more seems excessive for what it is, I'd have thought £35 would be more reasonable. The next photo shows the plastic spigot on the clutch release bearing which pokes out the bell-housing. There's nothing special about it, just an o-ring in a groove close to the end, and further back, another groove where the retaining clip locates. There are no seals or o-rings in the metal block that pushes onto the spigot. I replaced the o-ring with one from my box of assorted o-rings (box of 85 for £2-20 from a DIY store).
The retaining clip appeared to be broken, as some parts I found in the metal bit looked like they'd snapped off. It could be this wasn't holding the hose on firmly enough, hence the leak. I pushed the hose back on and strapped it on with some cable-ties. I also put a larger o-ring on the spigot, to fill the gap at the end. I pushed the clutch in and out a couple of dozen times, felt around the hose joint and it was dry, so I'm hoping this has stopped the leak. If I had bought a new hose, I don't even know if it would include a new o-ring, it might be classed as part of the release bearing. I'm certainly not going to buy one just to get a new retaining clip, I think I can come up with a better solution myself.
