On the A14, I’ve noticed that when it’s shut, and the official diversion is ridiculous, but there’s a much shorter, unrestricted route, they often place a mobile speed camera on that shorter route in the early hours. So bear that in mind. There’s a chance they’ll put one in Barton Seagrave somewhere.
I was doing 23mph in a temporary 20 zone up by Felixstowe one night last year. Never heard anything back, but I bet there were plenty doing 30+ who did. Also saw a mobile camera at 2:30am in Stowupland near Stowmarket a few months back.