Interesting thoughts and information about the UK green petrol problems in the comments on that story further down.
The contaimination is silicone oil, reported on ICIS News (and elsewhere). (I work for ICIS: About ICIS). What interests me, and I'm sure that Tesco, Morrisons, Greenergy, Vopak, who ever shipped the ethanol (and anyone else up the supply chain that I've forgotten) will want to know is: how the silicone oil got into the ethanol.
About the only thing that can be said about silicone oil in this context is that it is oily. It is not remotely similar to ethanol. It is also very much more expensive than either ethanol or the other components of gasoline.
My guess, and it is pure speculation, is that there has been some at some part of the supply chain, and maybe a low viscosity silicone oil was used by the maintainance person to lubricate the seal and to position it. It's siliconE not silicon. (I remember because one is oilE the other makes computer chips). Just to confuse mateters there is silicon in silicone and they'll be testing for the element silicon. .
I particularly like Mark C's plan of getting two independent people to examine the problem and report back, which would be partly funded by the two Supermarket companies. But this may not be necessary if the paperwork is in place and hasn't been tampered with...
Postman Patel gives a roundup of fuel ethanol issues...