Looking at the grass verges, kerbs and the wear and tear to the surface of the carriageway it is at least 10 years old, how about the A40 between Denham and Beaconsfield? Only a wild guess as that has a couple of stretches of dual carriageway.
Gene the newest still you have posted ,with the parking sign visible, does remind me of the A414 heading towards the A5/A405 roundabout, last one before the M10, that lay-by had a 24 hr cafe in it, a static caravan if my memory serves me correctly (anybody remember it?), but it has been nearly 30 years ago since I done those night trunks to Argos at Welwyn Garden City from Penkridge in a Leyland Cruiser 16.15 or a 16.17 if you was lucky, so I can remember every little dip and rise in the road,as it meant a left leg and left arm work out!, those under powered heaps would have gotten in the way of Stepoe’s horse!
Then again it could be Buzzer “road racing” his Baldy 'Oss ! But he is either that far in front or well beat as the attendant crowd of Itinerants are not in close attendance in their shiny motors ! But he could be just out training for the next “match” 
pete smith:
Gene the newest still you have posted ,with the parking sign visible, does remind me of the A414 heading towards the A5/A405 roundabout, last one before the M10, that lay-by had a 24 hr cafe in it, a static caravan if my memory serves me correctly (anybody remember it?)
Pete. I’ve got square eyes through staring at Google Street View
I think this section of the A414 is the closest thing yet. In the film it appears that the Pickfords van in picture 2 is about to go over some sort of bridge, and now, on that section you mention there is a bridge - albeit a more modern build going over the River Ver. There is also a lay-by on the opposite side (which is now also an entrance to a house (Inglewood Gardens) - but above all the road shape also fits.
Unless anyone can come up with an alternative I think this is as close as we can get.
Thanks again to everyone for their helpful suggestions. Very much appreciated.
Cheers.
Is the Pickfords lorry part of the film, I only ask as there is a similar Pickfords lorry in the funeral scenes filmdope.com/forums/112854-help- … tions.html
Dave…
Yes Dave. There are two separate scenes in the film that use Pickfords lorries. In fact, Pickfords tweeted a still from the film quite some time ago and asked if anyone knew what the film was called and where it was filmed. I replied with the info and they thanked me.
I submitted lots of film locations for the website you linked above (It used to be the Brit Movie Forum) as well as other film location sites. I now run my own Retro TV/Film/Motors/Music site. It’s called 4:3tv - The Retro Forum which you’ll find here :- http://43tv.proboards.com/.