Another update on this:
The car has now become a bit of a dog.
It is still very hard to start in the mornings. I would guess that the recent very cold weather hasn't helped, but it has nearly flattened the battery trying in recent weeks.
The crankshaft sensor failed a month or so ago. I bought a replacement one and fitted myself. Cost was around £25 and it took around an hour to fit. (Although the car was still under warranty I would still have to pay the diagnostics charge - £35 - and seeing as I have the diagnostic equipment myself, then I would be £10 down to start, and it was easy enough to fix).
During the snow, the ABS light came on. I read the fault code and did a bit of research, and the solutions that came back all pointed to people replacing the ABS ECU.
The rear wheel arches are also starting to bubble with rust, as well as the front doors.
I've lost all confidence in the car, as it seems I can't drive any further than 30 miles without the engine management light coming on. Normally stopping the car and restarting will extinguish the light and stop it coming back on, but I'm always expecting to look down and see a little orange light on.
I'm now looking to trade the car in at a garage. I know I'll take a hit on the value - I've been advised around £1000 on a trade in, meaning I'll lose around £1400 in the 5 months I've owned it.
Unfortunately, I think it's probably worth it!
Last comment on the Vectra B, it's being traded in tomorrow for a 2008 Vectra C.
It's leaving me with a parting fault though, - the fuel gauge seems to stick when it gets to 1/4 full.
If you park up, then it can be reading 1/4 full, then the next time you start it up, it will have dropped off the scale and the light is flashing. You have approx 3 miles before it becomes totally empty. I've run out of diesel once, but luckily it was very close to a petrol station.
I know it's a big price jump from a 2002 Vec B to a 2008 Vec C, but hopefully it will be nice and reliable.
On the plus side, I was cleaning it before it gets traded in, and it is a good looking car, and the 1/2 leather interior is excellent.
I had the same fault. Look in the engine bay for thin black pipes, follow all and check all rubber elbows that attach these pipes to the various solenoids they connect to, as they corrode... do this thoroughly, and this will solve your problem deffo... make all air tight again, and you will be a happy man. This fault causes false air temp an pressure readings, sending the ECU mad!