Im heading to Devon early in the morning and will be coming off the M25 onto the M4.
Other times ive driven this route (usually to Bristol) the signs on the over head gantries have sead M4 J4B closed for roadworks. But when ive got there ive not had any problems. Usually i hit the M4 just after 6am admittedly.
Is the junction closed before 6am or is it open through the night now?