This was a titled a "Mystery Bus" - There was conjecture over this vehicle. Originally it was thought to be possibly a Plymouth Regal IV (circa July 55) or maybe a Reliance. It was questionable whether it was destined for New Zealand or a small U.K operator.
The mystery is now solved!
The following analysis was kindly given by Malcolm Tennant (a member of the Management Committee of the Scottish Vintage Bus Museum at Lathalmond, near Dunfermline).
Malcolm's perception of this vehicle was that it had a striking resemblance to a 1954/5 AEC-PRV Monocoach of SMT (by then officially renamed Scottish Omnibuses Ltd.).
He commented: The SMT livery layout (of light green lower panels with darker green wings and cream roof, waistband and wheels ) seems to be echoed here. Only the absence of the "SMT Diamond" fleet emblem on the side and the "not-quite-as-I-remember-them" rear end causes doubt in my mind. I recall that SOL Monocoaches had twin side-opening doors to the boot, rather than a lift-up flap, and the number plate aperture doesn't seem quite right. However, as Scottish Omnibuses purchased the first six production Monocoaches (MC3RV001-6) and then 50 more in 1954/5, this may have been one of the first batch pictured prior to delivery (and presumable modification).
Now a further analysis by Neil Fraser (please see his AEC site) has confirmed that it is indeed a Reliance.
Neil has suggested that the "mystery bus" is an AEC Reliance MU3RV008, a very early production chassis, with Park Royal body number 39147. In Nov 1955 this vehicle was an exhibit at the Scottish Motor Show and was in Scottish Omnibus livery. It was later registered HSD 473 and sold to Hogarth, Ardrossan, t/a Clyde Coast Services.
So is the mystery now solved! It is certainly an AEC Reliance and a UK Coach after all. And if anyone has any further information then I'd be pleased to hear from you.