The battered coach may be precariously balanced on the side of the bank, but the message is very clear: this crash could have been a lot worse.

The blue and yellow express coach came to rest at a 45-degree angle on a steep embankment. There seems to be no reason why it did not simply roll over and over into the ditch below.

The bus, carrying holiday-makers from Terminal 4 at Heathrow Airport, appears to have struck a stationary recovery vehicle and slid along the hard shoulder before plunging down the bank 30 metres away.

Its door is ripped off and the side panel peeled back like a sardine can.

The windscreen has been knocked out and the driver's seat has fallen forward, while the first two rows of seats lean slightly to the left, away from the crushed corner of the bus.

The carriageways are strewn with plastic and debris, with the crumpled toilet from the bus lying in the road.

Small bottles of French beer spill out on to the Tarmac where the side of the lorry has been ripped away, and the truck's bonnet stands open where the mechanic has been working on it.

Police cars have blocked off the northbound carriageway but early evening traffic speeds past in the opposite direction.

The scene takes on an eerie quietness as it begins to get dark and policemen in fluorescent jackets start taking measurements.

As the light fades, officers prop up the bus to stop it rolling further down the bank and reopen one lane to traffic heading north from London.

It's another day's work in the life of a motorway patrol.