Have you checked for leaks?
Have a look see if the fluid level in the reservoir has dropped.
If the level is ok would guess the master cylinder is at fault. Was it a new one fitted or second hand?
Sorry to answer James's question, but yes on the solenoid. It will spark a little, but if engine turns over you know engine and starter motor are ok. So the prob will be the solenoid or the feed going to the solenoid. Hope this helps.
There are a few fairly local, around Southwell, a bit scratchy but nothing to testing. Will let you know next time were going. Where abouts in Notts are you?
I would imagine the pedel going soft was your brake fluid starting to boil, once you have sorted binding brake bleed the brakes. Some new fluid should solve it .
Had very simular prob with my series, ended up air leak. Get some carb cleaner and with engine running spray around the carb, this should hopefuly help pinpoint the leak.
Mine had 2 one was carb insulater the other wad the accelerater jet diaphragm. Hope this helps.