My 91 1.7 340gl has just today started to idle very badly.

it idles fine then almost dies, then picks up a little and almost dies etc etc. once revved up a bit it runs fine for a bit then back to the same. only thing that has changed recently is the choke cable has come loose from its bracket at the carb, so i have no choke control but the cable is still attached and the sheath just moves if you pull the knob instead of pulling the choke lever.

any ideas appreciated

Are you sure the chock is returning all the way when closed?

Why has the choke cable come loose?

A known problem with the carb is the base warps, causing an airleak. If you grab the air filter box and give it a wiggle you can feel if something is loose (either the warping, carp top plate coming loose, air box itself being loose). Any of those will cause a rough idle, as would an airleak in one of the associated hoses around the carb base.

FWIW, if the car starts with no choke when cold (i.e. even mornings in the summer) then it's running too rich, so get the choke fixed ASAP.

This does sound like an air leak at the manifold/carb flange, cyclic surging, no actual idling.
spray some wd40 around the carb flange when its running and listen for the tell tale slurping/watch the wd40 get sucked in.