Wouldn't have thought you'd get a course as you're over half the speed limit again. I was clocked at 45 entering a 30 (same scenario going from 50-30) but fortunately it was one of those community speed watch programs so only had a visit from the local PCSO.
Had something similar from Fairford to Lechlade.. Coming off the roundabout and it's 40 and then drops to 30 shortly after. My own fault, I wasn't paying attention. The police were showing kids interested in policing how the gun works etc. I was caught doing 42 in a 30. Had a stern telling off and letter through the post.