There is currently no left turn from Wood Street into High Street, and no corresponding right turn in front of the parish church from High Street into Wood Street.
Within hours of the temporary suspensions taking effect ambulances heading south along High Street were forced to do emergency U-turns and then, with blue lights flashing and sirens sounding, had no alternative but to drive on the wrong side of the road towards oncoming traffic as they headed for Barnet Hospital.
The aim of the trial, which might last anything from six to 18 months, is to assess the impact on traffic flow at the junction in order to see whether it might be possible to widen the pedestrian refuge in front of the church.
When Barnet and Southgate College opened its new campus opposite the church six years ago, a condition of the original planning approval was that the college had to provide funds for an improved pedestrian crossing at the Wood Street-High Street junction.
Barnet Council had arranged for the trial to start in February or March. No explanation has been given for the delay.
There have been some estimates that as many as 400 vehicles a day execute either left or right turns at the church, and their suspension will force extensive detours.
The Barnet Society has suggested that it might be possible to redesign the pedestrian crossing while retaining the left turn from Wood Street, but the Council says this is not possible due to sequencing of the traffic and pedestrian lights controlling the junction.
The difficulty facing ambulance crews is likely to be replicated by lorry drivers whose satnavs indicate that a right turn from the High Street is still possible at the church.