Variable Speed Limit Change - Friday3732

Hi, first time poster although an avid reader for some time. Driving along the M42 near Shirley last Friday which is covered by Variable Speed Limit Camera's, traffic is light & as I approach one between J4 & 3a they change to 50 limit. Quick look in my mirror & a car close behind so choose not to brake (my speed about 70) but to lift off for a few seconds. I didn't see a flash but what do you think? I have a dash cam fitted thankfully which I will show to the court if needed www.youtube.com/watch?v=gymqsEDDMJo

Thanks

Variable Speed Limit Change - daveyjp
From info provided by Highways Agency there is a 60 second interval between change of limit and cameras activating.