According to the online official checker for this charge my 2003, 3.2 Omega is exempt as it meets the criteria of acceptable omissions.
Quite simply if a petrol engine meets Euro 4 compliance when built it is ULEZ compliant. Same rules for all CAZ and ULEZ, nothing has changed there since their inception so yet another no news story from the press.
What the news should be reporting is how a scam such as this can be legal - If Khan really cared about the environment he would ban all so called 'polluting vehicles' from the ULEZ zone and provide a so called 'green' alternative, but. there's an opportunity to scam people out of money who have no means to meet the vehicle criteria.
Just to add insult to the situation, Westiminister City Council (and probably others) add a surcharge to park a non-ULEZ compliant car.... Not sure what they are smoking but as far as I am aware, a vehicle without an engine running (because funnily enough it's parked) doesn't produce any tailpipe emissions.