Diesel bug in BMW 7 Series - any advice?

I have been told by my BMW dealer after spending £1000 that the reason my car stops running is that I have a diesel bug that has damaged the high pressure fuel pump and now has put small bits of metal into the fuel system. BMW say that the whole fuel system will now need changing at a further cost of £7,000. I only ever put Shell V Power Nitro Diesel in the car from the same garage. The garage say it has not had any problem with water in their fuel tanks. Shell Head Office say they have no other complaints in the UK of fuel contamination from a diesel bug although the BMW dealer has sent photos of the diesel bug in the low pressure fuel tank like tar and a photo of the inside of the fuel tank showing the metal bits. Do you have any advice?
This explains what 'diesel bug' is: www.ipu.co.uk/diesel-bug/?gclid=CJnB2-iJ0ckCFQupGw.../ I never called it that. I always called it 'globules of emulsified fuel'. But I have never heard of it breaking up a low pressure immersed lifter pump and anyway any shards of metal pumped through would have been caught in the diesel filter before it got to the high pressure pump. What could have damaged the high pressure pump is excess moisture in the fuel leading to a lack of lubricity that resulted in the pump grinding metal to metal. You don't say how old your car is, how often you fill it up, or what sort of mileage you do. If you do a very low mileage, then it could be that your tank became contaminated.
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