This could well be a situation where the copper tape that keeps slugs and snails out could come into its own. I've never used it as I don't have pots that need this sort of protection, but I think you stick it round the top of the pot and it keeps the pesky critters out. You'll need to check several times at night after you've stuck it on as there may be slugs and snails snoozing the day away inside the pot already.

With a bit of luck and TLC you should be able to revive it. In the meantime, before you get the copper strip organised you'll need to go out after dark with a torch and pick off the culprits. (They'll slither back unless you stamp on them or drown them in salty water)

Strange how they love cytisus - you wouldn't think the leaves would be big enough to interest them, but they seem to love it. I would add a few wildlife friendly slug pellets to the pot as well as using the copper tape, to catch any still in the pot that you might miss on your evening snail hunt.