How do you get a broken glow plug out of 106 1point5 diesel?

To remove a broken glow plug can be difficult, especially if the head is still fitted to the engine and still in the car. If you can gain access to a mig welder and an appropriately sized nut, you can weld the nut to the remains of the glow plug, allow to cool and then using a socket carefully ease the plug anti clock wise, then clock wise to help break the bond that has formed between the threads. If the head is on the bench this task is much easier, failing this you can have the plug wire eroded out of the head (whilst leaving the threads in perfect condition)but this can be expensive.