I dug a little deeper and found that you have to apply to BMW by emailing a form and a copy of your reg doc and they will enable the car.
When I log into the site
https://www.bmw-connecteddrive.co.uk/ I can now see my car. However I don't seem to be able to do anything with it without buying a subscription for ConnectedDrive Services at £120/yr
I had hoped to be able to use the BMW remote app on my mobile, I can now log in to the app and see my car, but there are no options to do anything with it, presumably because I need ConnectedDrive
Is there anything I can do with this without the subscription ?
Seems a lot to pay (my road tax is only slightly dearer) for something I guess I can easily live without - just a shame that for most people it'll be redundant once the car's three years old