Start car, no problem, headlights are on at this point without switching them on, indicators and hazards don't work, no reverse beeper, no flashing indicator at lock/unlock, dashboard lights not illuminated, any ideas as to what these faults have in common?

They are all electrical faults

Try disconnecting the battery for 30minutes, reconnect and see if anything changes or gets worse.

Steve, you say the dashboard isn’t illuminated, do you mean the digital displays or the background lighting to see the dash at night? If it’s the latter all your problems seem to be lighting related, and my guess would be the lamp control module. This module is mounted down low in the drivers footwell behind the kick panel on the right. This is also an area which can suffer water ingress through the o/s A pillar. Might be worth removing all the trims to get to the module, and checking for signs of water tracking down into the module. If that’s the case, you lighting woes can be sorted with a replacement module, but you’ll have to find and fix the source of the water leak first.
Only an educated guess, but that could well be what’s linking all the faults you describe.
Let us know how you get on.

All the digital lights are on it's the background light that isn't, I'll have a look at your suggestion and keep you updated

Early last year my SC had all sorts of electrical weirdness happening due to a faulty Lighting Control Module. A new replacement was expensive enough for my brain to have totally deleted the actual cost though.

I found a guy on eBay offering a repair service for £69.95 – you send your faulty LCM to him and he repairs it, no recoding to your car required, no black dot next to your odometer reading (the LCM also controls the mileage reading so if you install an LCM from a lower mileage car it puts a black dot next to the mileage to indicate it’s been clocked).

Mervyn Ashton at AutoElectron in N.Yorks. The current eBay listing number is eBay Item No. 283844982047 but please check this is correct for your car.

Good luck. 2006MY 4.2 SC
BMW R1250 GSA Rallye TE
Triumph Tiger 1050 (sold)
1979 Pontiac Trans Am (sold)

Cheers mulcher I will check it out👍

Well, bizarre chain of events, I realise that the battery is usually the first port of call for on the fatty, so although the one fitted is only 2 years old I decided to return it for an exchange, swapped it outside the shop and low and behold everything back to normal, this in spite of the salesman testing the old one and saying it was ok, very pleased 😁😁