...not just when cold, but odd times, usually with foot off accelerator when braking to stop (clutch in, naturally!).

I wonder if it might be a fuel filter blockage? If so, where is the filter, and is it washable? Having just been off-roading, I wonder if it's shaken up the sludge in the tank & some dirt has sneaked down the fuel pipe? Or, is it more likely to be a fuel injection problem at the main butterfly area? (Can't remember what that chamber's called).

Getting worse, whatever it is - cut out as I stopped before passing a stationary truck today, wouldn't restart for a few seconds, then ran as if nothing had happened, only to cut out again six miles later when entering a roundabout(I bump-started it that time, using the momentum to keep going, though it coughed a bit).

Any clues, folks? All advice appreciated...