Mini clutch arm stuck open

Just remembered a trip back from a Mini event at Silverstone. After an hour or so of elevated speeds in my Mini Minus, I swooped down a slip road on the A14, went to add some engine braking only to find the clutch pedal locked solid. The locknut on that shaft had come loose allowing the flanged one to rattle up tight to the cover. Bit of a moment scrubbing off the speed before knocking it out of gear and pulling up for a look see. Of course I had two 15/16” spanner’s and a torch… not.