Thanks for your replies.
I've been in touch with BMW again and have had this response:
"Good afternoon David
Thanks for your further email and your patience while I’ve looked into this for you.
When this bike was manufactured (2006) there were no requirements to allocate EU emission compliance certification or publish such emissions data as it wasn’t enforced yet. As such this bike hasn’t got an EU emissions standard rating allocated to it.
With this in mind, during this time bikes where generally manufactured to EU3 standards. But, I can’t guarantee this is the case for this particular bike.
I hope this helps and if there’s anything else I can do for you, please let me know.
Kind regards"
I think Transport for London assume that all vehicles have an emissions rating, but as you can see, this isn't the case for earlier motorcycles.
At the moment Transport for London are considering motorcycles from 2006 onwards are going to be ULEZ compliant.
But......
Who knows they could easily change their minds
Their ULEZ Vehicle Checker is full of disclaimers, allowing them to change their minds, without any legal consequences:
https://tfl.gov.uk/modes/driving/ultra- ... ecker-ulez
I've seen a 2006 R1200ST that I quite like - might just go for that and keep my fingers crossed that Transport for London don't change their minds, again...