Motorists are experiencing sever delays between junction 15 and junction 14 of the M1.
Highways said at about 3.20pm that unplanned work is being carried out on the southbound road surface. As a result, one lane is closed.
A spokesperson said: "At present there are delays of more than an hour on approach.
"Traffic between Birmingham/ The Midlands and London is advised to use the M40 if at all possible to avoid these delays."
A knock-on effect is slow traffic on the A508 both ways between Grange Park and Roade as traffic diverts. There are also temporary traffic lights causing delays on this route.