Surely all your suggestions would stop the clutch disengaging TWR. I cannot understand how ditchy thinks the clutch is OK if the engine runs and the car doesn't; the only way that could happen is if there were teeth missing on one of the gearbox cogs or the diff/driveshaft/CVJ was jiggered.
I've just remembered a problem I had many years ago with a Maxi. That suddenly lost drive; the reason was that a drive shaft had popped out of the gearbox/diff casing. If ditchy is lucky it could be as simple as that.
Mine was NOT one of the OK ones. At the time it was the newest, lowest mileage, most expensive car I'd owned and it was nothing but trouble. It still holds the record for the car I've owned for the shortest length of time.
There's no drive, so the car isn't going anywhere. The speedo cable comes from the "back" of the gearbox so, if the lack of drive is due to the clutch the gearbox doesn't turn and the speedo reads zero. If the drive shaft has gone the gearbox turns, the speedo registers the speed but the driving wheels don't turn.