This is solved, but might help others.
On the first drive after three weeks standing, the acceleration is underwhelming, braking is terrifyingly poor, the disks are overheating madly, and the clutch slips for a couple of seconds after take-up. How do three things go wrong all at once?
The cause is so simple: the brake and clutch pedals have bound to their hinge-pin in the pedal-box. So the brakes are half jammed on and the clutch comes up only s-l-o-w-l-y.
Brutally (there's no other way to make it move) bash the pin half-way out. Liberally oil it and rotate it a few times. Lightly press it back in. Two free pedals. Happy days.
