Thanks for that Richard. I agree there should be negative pressure here from the turbo sucking. The engine breathing heavily would also explain why there's quite a lot of oil in the pipe.
I would clean the turbo spigot and pipe well with meths or something to degrease it, then crank the jubilee up with a socket.
I've done exactly that - still comes off.
It's worth pointing out it's not any old jubilee clip but is a worm-drive type clamp that is perfectly matched to the shape & size of the orange sleeve.
I can't see any difference between the one on mine and the ones you see in a google image search for "1.6hdi turbo". Looks like a fairly standard jubilee clip - which is a worm-drive.
Are you still intentionally overfilling the oil?
I have it just below the maximum level marking.