Well, got the Z4 back last night. Big difference in starting now! Hardly turns over and it fires!! Also seems quicker on pick-up! On reflection I don't think that fuel pump has been right since I've had the car seeing how it pulls now!
Dealer said it was a sensor that was changed before, not the fuel pump so this is the first time it's been changed. Dealer also doing the "we don't know of any national problems with the high pressure fuel pump because if there was, BMW would have done a re-call" at which point I showed them the article on BMWBLOG about the recall in America at which point I was told "they have different parts over there!"
Basically I had to pay the £100 extended warranty access to get the car back, even though I argued that I tried to book the car in when it was in warranty and I had reported this fault in November last year, at which point the dealer couldn't find anything wrong!
They are contacting BMW about this, but I'm not hopeful of getting the £100 back!
Still. car goes well now so the Audi may have to wait a bit longer!
I would suggest anyone who's warranty is running out soon to take the offer of the extended warranty (god knows how much I would have paid if I hadn't!) and also get that high pressure fuel pump checked out (although until it shows a fault code, I guess they can't detect it!).
Just noticed I posted this in Jan on here:
http://www.z4-forum.com/forum/viewtopic.php?f=45&t=33537