Noticed my clutch was very hard to depress yesterday, then this morning there was a little travel in the pedal before engaging the clutch, then more an more until the pedal travels down to the floor an springs back up to the top with no resistance.

Have taken the Master and slave cylinders off as one piece and all seems fine with that, not sticking, and returns to the normal position.

The rod that is pushed by the clutch cylinder (at the gearbox end) only sticks out about 10mm, which doesn't seem enough.

Sorry about the non technical details, I'm handy with a spanner but don't know what the things are called.

Cheers.

suspect the arm is fooked, worn through - dead, gone to meet it's maker

Please excuse my ignorance! But when you say arm, do you mean the fork bit that pushes against the thrust bearing part? I'm guessing it's a gearbox out jobby

Are there any illustrated guides to this anywhere?

i think by the sound of it that is right clutch fork
i think buster has a post on a clutch renewal dont quote me but you will find a guide or just ast and i am sure we will help

http://www.landyzone.co.uk/lz/f7/defender-gearbox-removal-clutch-replacement-pics-136171.html
this might help