I thought I'd share a few photo's with you of the offending loom in question.
In the light of day it appears that a cable tie may have become broken /removed for whatever reason allowing said loom to sit on top of the coolant pipes and had melted the outer plastic conduit and eventually had melted thro the cables within.
The photo's show the position of the cable and where I believe the cable tie should be as now shown.
Cable under Pipe from air filter
Easily seen without intake pipe
Cable tie fixed to bracket on coolant pipe.
There are two fixing points this is the second one ensuring loom is kept off coolant pipes
This is where the loom was resting on the pipe and eventually melted thro'. How long this had been going on I've no idea. I never noticed it.
This is the fuse it kept blowing (30 amp) in my case No6, but I believe in later models this maybe No2
It might be worthwhile you checking your loom as it is quite a tight stretch and is a little awkward to reach. At the weekend I will remove the engine cover again and disconnect the loom from the various sensors allowing me to redo the loom and add more of the protective covering and tidy it up a little more in daylight to ensure I don't have any further issues.
Like I say I don't know how long it's been going on like this. The only time the loom may have been moved was when the head gasket was done along with the cam belts and pump 12 months ago.
Guys just check yours when you can the clip/tie could have been missed broke I don't know but it caused me enough headaches.