Many thanks. I had seen this, and the result for the CB500. Unfortunately, I need to tax, MOT and insure the bike. With the additional £175 for the emissions test, I haven't had the spare cash to get this done. Will definitely do so in the next couple of weeks.
@Avidfan have you seen this?
https://www.bikerandbike.co.uk/how-to-get-a-motorcycle-emissions-test-and-beat-the-ulez-charge/
this site has also compiled a list on non-euro 3 bikes that have passed and the cb500 is one of them
https://www.bikerandbike.co.uk/list-pre-euro-3-motorcycles-with-ulez-exemptions/