TBH I never bothered to contact my local dealership for a cost of the sensor (I have a little history with them and will avoid them whenever possible) - but knowing the +BMW tax it will be considerably more than the £60 incl vat that I have paid at my local motorfactors (I do have a trade account).
The part number for the genuine item for BMW is 11787672785 and the NGK/NTK part number is OZA630:BM2. As NGK make them for BMW I really didn't see the point/need to return to my local dealership and allow them to take my pants down!
I just thought that I would take the opportunity to thank those that commented, provide some "useful" information on the component and hopefully help anyone else out who may have similar issues with a resolution.