Did you replace the battery, before your 4 week trip? or after?

After my trip. Infact, I just replaced it in December. From September to December it started fine after jump starting it. Then it started playing up in December and I had to jump start again. I then decided to buy a battery.

I'm confused. if they said pressure to fuel rail is fine, why they suggested fuel pump might be the cause?

They actually could not replicate the problem. The weather was about 10C.
When I picked it up it started fine.

Now it won't start again they are saying a fuel pump. Does that sound correct? Maybe now that it won't start they will see the pressure is not getting high enough when the fuel is cold.

how the relay for the glow plugs??

I'm clutching a straws - I saw the last thread on http://www.bmwland.co.uk/talker/viewtopic.php?t=64944 & the problem was solved by cleaning/replacing the fuel pump relay.

BTW: Its 2004 with 40K miles. I've owned it for 2 years and last winter it was fine.