Worst ive seen that.

Extra crispy lol. I can smell that from here...

Looks like it might have been arcing too.

This have nothing to do with a stuck starter or the Earthing of the fitting. Starters overheat like this when the weld of the bimetal strip inside the glow lamp fails, and the strip detaches from the post. The lamp then will glow continuously without anything that would close the contact and extinguish it, so it heats up until it sets the plastic on fire

That’s quite bad

Ash, the unearthed fitting will not help, as from my experience when they get like this they usually track to earth and trip any RCD protection or trip the circuit protection. Not having any earth will almost certainly have allowed this to go on for longer than it might have done otherwise & make a bigger mess!

Ive only ever seen this from starters continuously trying to strike EOL tubes and overheating plus starters that just stay lit all the time.

The tube fitted was an EOL Sylvania, it had probably been flashing away for a long time... I've fixed this now, removed what was left of the old starter & holder, used some mildly abrasive cleaner to get the worst of the carbon deposits off and fitted a used BJB starter holder from an 8ft fitting I scrapped recently. Good as new now (ish!)

Good work!

Only problem now... I have no lamp holder springs for this fitting as I robbed them for use on another one, doh! Never mind, should have something in the parts bin that'll do the job hopefully

In my Fitzy's the starter holder is something unique that mounts to a square hole in the back of the lightpack body. I don't know of any other starter socket with the same mounting. Are the newer lightpacks different ?