Was the new fuse box / consumer unit put in by a qualified NIC-EIC or NAPIT electrician who supplied complete certification of the work/installation ?
an Insulation resistance test for that circuit
will be should be
on the certificate
along with any departures from BS 7671 (wiring regs)
have you had the light replaced since ? extractor fan running off the same pull cord ?
"the insulation was black and burnt like it had been on fire" sounds like insulation break down (due to overheating) ,loose connection , or overload due to under-size conductor
I dont believe this has happened since we own the house
how would you know
but my question is we have a upto date board that was put in a couple of years ago if this fire happened now would it trip the board out. Also it looks like the yellow green wires are not connected to anything would this have cause the fire.
Even the very latest board with SPDs ,RCBOs, even AFDDs is unlikely to trip if the cables and connections are in poor condition or badly installed .
Yellow/green wires = CPC = Circuit Protective Conductor = "EARTH"
if class 2 (double insulated/plastic fittings, designed to operate without the need for a CPC/EARTH) fittings & switches are used then the CPC just protects the live cables .
As you are asking such questions ,I'd suggest you find a qualified electrician who will do a full PIR (periodic inspection report) and advise you what works are required to stop your house burning down /electrocution/shock etc .
better to be safe than dead