Further to the comments on the Time Trialling Forum, I have driven the course this evening (10th June) and there are no roadworks/lane closures in sight nor any signs indicating any works in the near future.
Also, Bucks CC have told me that there are currently no roadworks planned on the course on 12th July. (There are lane closures for 3 days in June and 3 days in July but not on the date of the event). I will drive the route again on 29th June to check.