A FOUR-VEHICLE smash has blocked the A1(M) between Welwyn and Stevenage this morning (Thursday).

The accident on the southbound carriageway happened about three-quarters-of-a-mile south of Junction 7, the turning for Knebworth House, at 8.20am.

The cars involved were two silver Vauxhall Insignias, a grey Volkswagen van and a blue Volkswagen Passat.

One lane is blocked and traffic is backed up for miles, back past Junction 8, for Hitchin.

The Highways Agency said normal traffic conditions are expected from 10am.

There were no reported injuries in the crash.