Ah ok makes sense:
W reg (2000) 2.8 FWD. Not a sport although has 18" sport wheels

2000 should be the "drive by wire" throttle where cruise control is just a bit of software in the ECU. Earlier versions actually had a separate box in the engine bay ECU box and that really could go wrong.

As such, with DBW, the switches on the stalk talk directly to the engine ECU and are pretty simple.
They often get gunged up, spraying with contact cleaner and energetically exercising them can often bring them back to life.
Unless of course they really are broken, but all that VCDS (or any other diagnostic) can tell you is whether it sees the switches operate, not that they are "broken" so this is always worth a try.

Do any of the cruise control functions work ever? Mine didn't when I got the car and it was the end button that wouldn't "set" a speed, so it never worked until I cleaned and "exercised" it. ;)

That's interesting, I'll have a play with the set button. Thank you!!
The previous owner mentioned that the 'set' button worked, but you could increase the speed. None of the cruise control has worked since I've owned it, which is since May only. Best car I've ever had for motorway duties.

Mine's still not great on increasing speed (or resuming), sometimes it just disengages.
So I'm more in the habit of increasing with my right foot (which is actually easier than that horrid little slider anyway) and pressing set again.

I think my slider switch is the least reliable bit so I just leave it permanently in the "on" position. Beating the hell out of the end button got mine working reasonably reliably in the end and you can live without the rest.

The garage have stated that the faults are from the throttle body, so a new one is being fitted. £350 for a new genuine Bosch item. The main dealer wanted 900 quid!!!

I don't know if a logged throttle body fault would inhibit cruise control, it just might, so try it again after the repair.

TB replaced, seems to drive well and idle better with a/c on; but that might be placebo.

I'll have a go with the cruise control later.

One other thing: with regards to the plastic box that sits in the bulkhead on the passenger side, it cotains the abs and tc ecus, os it possible to purchase a new seal to prevent water ingress? Or should i just silicone seal it?

I had a lot of similar trouble some years ago. The TB was replaced and all seemed well - until it rained heavily again (I was in Scotland at the time, so didn’t have to wait long! :) ) and the strange symptoms restarted. In the end, the garage took that plastic box apart and discovered signs of serious water ingress. IIRC, the seal was available as a new part, but it may have come complete with the lid.

Unfortunately you can't buy the seal by itself, as it comes as part of the cover. The part number for the cover is 4D2937128F and cost around £50... if you can find one in the UK. Failing that, you can still get them online from either of these two sites:

E-ACCA.COM @ 44.99 Euro

carparts-pros @ 53.30 Euro

And if you don't want to go down that route, there are a few secondhand on eBay around the £20 mark, although you'll have no idea about the state of the seal.

Hopefully it's not unlike the seal around the air intake and that you can easily buy a roll of suitable adhesive foam strip. ;)