BMW 320D Starting Problems

Hi, My 52 reg BMW 320D has developed a cold starting problem this winter. Basically, depending on how cold it is, it can take a long time to get the
engine started. Once started no problems until the car is left for while (usually overnight). I've had the car in the dealer twice now and they still haven't resolved it.
First visit, diagnostics reported a couple of glow plug fault codes. They replaced the two glow plugs, and tested the injectors. All fine now they told me. But nothing changed, problem still there.
I noticed that when the car would not start, if I kept turning the ignition on/off, after a while I could hear a slight whirring noise like a pump or fan start, and then the car started straight away.
I took the car back to the dealer, and explained the symptoms. They checked overnight and came to the conclusion the "pre supply" pump (which pumps diesel to the engine ?) was not starting when cold. They replaced it, and again told me everything was fine. You can guess it was not... again.
The car still fails to start easily on cold mornings, but once I hear the faint whirring noise, it starts straight away. So I suspect there might be a relay that switches the pre supply pump which is sticking ? I'd replace it myself if there was a Haynes manual for the engine to show where to look for it but there's not.
Does anyone on the ng have any knowledge about the pre supply pump, and if there is a relay switching power to it, and where it is ?
Thanks Tony
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the pump relay is the left hand of four below the dashboard somewhere.
I would be looking at an air leak on injector spill pipes if it was a Vauxhall, but I am not familiar with beemers
Mrcheerful
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