Grab it with pliers, twist and pull.
The glass envelope will almost certainly break and you can then drill out the remains of it.
Working inside a clear plastic bag will catch all glass debris.

Martin

Thanks for your help Martin - much appreciated.

I gave the the light bulb a pull and a twist and it broke as expected.  The plastic bag idea worked very well.  I didn't like drilling into an area that I new nothing about but persevered slowly and carefully.  I then noticed that the long part was starting to move and with a bit of coaxing it pulled out of the black lamp holder.  The photo attached gives a better idea what is inside the assembly.  The lamp hole is inside a clear plastic part - now looking decidedly opaque so the next step will be to clean it out and hopefully let some light through.  The lamp sizes I have are 5mm diameter so the aim is to end up with a 5mm clean hole.  Could be a tough one this time - it does look a bit of a mess after 40 years of over-heating.

Regards

Geoff