A section of the M1 was closed after a serious accident.

The motorway was closed between junction four, in Edgware, and junction 2, Fiveways Corner, southbound. It has been partially reopened and only one lane is open northbound.

A witness in a two-hour tailback said a badly damaged car lay overturned on the fast lane of the northbound carriageway.

The closure is causing gridlock on sliproads on to the M1.

More to follow...