Just had this back from BMW...
Dear Mr Cooke
Thank you for your further email.
We would confirm that, as discussed on the telephone, the oils that are recommended for your BMW are as follows:
Castrol TWS Motorsport 10W-60
Veedol Synthetic Z 10W-60
We can confirm that this is the same oil that is recommended for the M5 which may be why it is not easily available. We would advise that you should be able to get this oil from the Parts Department of your nearest BMW Dealership.
We trust this guidance will be of some assistance to you but if we can help you again at any time in the future, please do contact a member of the BMW Customer Information Team.
BMW Group UK
Product Information Advisor
Tel: 0800 325600
Fax: 0870 5050 206
VERY helpful. Also I'm not putting something that sounds like weedkiller into my engine
so I have ordered some Castrol Edge 10W-60.