"The National Police Chiefs’ Council (NPCC) lead for Roads Policing has suspended classroom-based speed awareness courses for 12 weeks, due to the Coronavirus lockdown.

"Motoring lawyer Nick Freeman has warned the suspension may cause many motorists who get caught speeding during the lockdown period to be issued with fixed penalty notices instead."

- from tinyurl.com/ybdacqow, dated 2nd April 2020, so you can work out that the 12 weeks are up somewhere around late June - this could be extended, of course.

Not necessarily relevant to the question but he had a pointed hat and no vehicle or signs and was in a group so I wonder if he could have been "having a go with a local group to show them how to use a camera"

Totally irrelevant. There is no requirement for a sign, no requirement for the officer even to be visible, no requirement for him to be wearing any specific headgear. Some forces are deliberately concealing speed cameras in the hope of more general deterrence, others go for very visible checks, also hoping for deterrence.

As a parallel - do you think it matters what uniform an officer is wearing when he arrests, or reports, someone for a different criminal offence such as assault or theft?

If you are right about your speed, it's unlikely that any action will be taken, as most forces don't take enforcement action until 10% + 2 mph above the limit, so 35mph in your case. Now the experience of the driver is another issue - the sequence will be (1) notice the officer then (2) go for the brakes and then (3) look at the speedometer. It can be, therefore, that at (1) we are looking at, say, 40 mph; then by (3) only 33 mph is showing; great sigh of relief by the driver followed a few days later with a letter from the police, and then followed by indignation: "I was only doing 33 when I looked at my speedo and they are saying I was doing 40"