Glow plug snapped

About 3 weeks ago my Defender 2.2 diesel , the Ford Engine one went into the garage to have the glow plugs changed, the mechanic snapped one off in the head , they are still waiting for a specialist to come and get it out, any one else had this problem, did they get the plug out without removing the head and what was the cost.
Thanks.

Not much of a mechanic if he can't work out the plug is going to snap in advance of it actually snapping.
They give plenty of warning, so another action plan can be put into place.
It depends on where the break is as to how successful the removal will be.