If this goes to court, tickets are irrelevant.
You can ask for a spicy meatfeast pizza, but it doesn't mean you're going to get it.
What he probably said was that obstructing an emergency vehicle is not a specific offence if you are not aware that you are obstructing it.
However, if he told you, on bodycam, that he doesn't think you committed any offence whatsoever, but he's going to stick you on anyway because who are the court going to believe, then you probably want to get a copy of the unredacted footage, including the earlier footage of him loosing his sh*t when Lord Lucan overtook him riding Shergar.
If hew was behind you for a significant time with blues and twos on, far enough back that he would have been clearly visible in your mirrors, and you failed to see him, that would seem to be evidence that your driving fell below the standard expected of a careful and competent driver.
That said, on the many, many times I have seen police with blues and twos being held up by oblivious drivers, I've never seen said drivers pulled over for obstructing an emergency vehicle, as the occifer had something more pressing to deal with - hence the blues and twos. However, if Morse had instructed Lewis to put the blues and twos on because he was fed up of sitting in traffic, he might be more inclined to stop and throw the book at someone who had failed to respect his authoritah.