Changed the clutch, clutch release forks MAY have been unmovable
Used excessive force to put the slave cylinder back in instead of bleeding some fluid off
Clutch pedal had no resistance until half way down, then it was solid
Pushed the clutch pedal EXCESSIVELY HARD a couple of times
<something>
Bled the slave
Very little resistance in the pedal at all other than a slight sponginess at the end of travel
Replaced the slave cylinder, was hard to bleed needing the bleed nipple open half a turn instead of the usual 1/8th turn, otherwise pumping the pedal by hand did nothing
Finally bled, closed the bleed nipple correctly (2 spanner method), put paper towel under the slave
Very little resistance in the pedal, no fluid leaking anywhere
Pedal is attached to the master cylinder
My master cylinder's shot ain't it?
0000218218 MASTER CYLINDER 31.12 GBP 35.79 GBP 35.79 GBP
0000215615 SEAL 1.52 GBP 1.75 GBP 1.75 GBP
Almost certainly not going to be able to get hold of it until at least Friday and I can't even put the subframe back on until it's fitted
Knowing what I know now about the gearbox's weight distribution, I chucked a nice pile of wood between the jack and the box which worked perfectly! Just slid the box out (the engine's still severely lowered and tilted) and pretty much just slid it back! While it was off I took out the release bearing to have a look at it and figured out what's wrong - that circular clip. Looking at the old clutch it was WAY too loose so it wasn't fitting through the pressure plate. Took it off, bent it back to a circle so the ~7mm gap was reduced to ~2mm, put it back on, shoved everything back together, cracked the fork down which really came back a long way, and as soon as I started to bleed the clutch I knew I'd got it 
I've operated the clutch (I presume) via the pedal!
I'm just sick of walking/riding/bussing to work 