Here’s a section for those photo’s of mystery motors, the ones you know little or nothing about.
This is my contribution to get the ball rolling, I know very little about it except that its a lady stood in front of an old Guy, (the rad badge reads “Guy Motors”), with an ‘FF’ registration - maybe 1920’s period which was issued by Merionethshire CC. The photo’s one I came across a good while ago on a flea market and just couldn’t buying resist it.
As Lloyd Groseman might say… 'Whooose Motor is this?" Any comments which would help solve the mystery would be welcomed.
If you have any similar Mystery Motor photo’s which you like solving, here’s the place to share them and hopefully get the mystery unraveled.
Cheers - RR
Hiya. Smashing old picture. No doubt you have googled it,
So have I 
The vehicle on the right has a notice in the windscreen saying it is a 1922 17hp 25cwt lorry, restored by Guy student apprentices, 1957
However the same website says:
in 1924 pneumatic tyres were introduced.
This next picture from the same site says In 1934 the very successful Otter light vehicle chassis was introduced, another first in a long line.
It had a payload of 6 tons but an unladen weight of under 50 cwt, thereby beating a statutory ban on vehicles of over 50 cwt unladen weight going at more than 20 mph. It cost £425.
In 1923 a 30 military lorry was produced and sold to the War Department. (A half-track vehicle was developed but was not successful). In 1926 a rigid six-wheeler with drive to both rear axles was produced and large numbers were sold as military tractors. About 1928 the Warrior 6 tonner lorry was introduced, the start of a long and successful line of vehicles under that name.
In the mid-1930s, at the Government’s request, Guys developed a short wheel base four wheeler general service truck — the Ant. This developed as the Quad-Ant gun tractor and as the first British rear-engined, 4-wheel drive armoured car. It also became the basis of the civilian Vix-Ant lorry.
So when I look at the picture next to the Pickfords truck, the split window looks similar, the earlier truck from 1919 looks too early. Also the front curved crossmembers on both trucks look alike. The tyres on your photo are certainly pneumatic but look larger than the 1924 model pictured, so Im thinking it maybe a later model or one of the early 1928 warriors spoken about, possibly with military tyres.
I think the louvred grille may help you to date the vehicle better.
Good luck in your search 
There must still be some sales records available. I wonder if Gaydon Transport Museum could help you.
I.m afraid that I cannot be of much help regarding the original query other than to agree with Wheel-nut. Try either Gaydon or The Black Country Museum at Dudley. I have been told that they have preserved Guy vehicles in there - they were made just up the road after all and are sure to have old time contacts on hand. The fact that it has pneumatic tyres could date it as post c1926 but many operators replaced the solids for a more comfortable■■? ride. Regarding the Pickfords vehicle. They operated very many of these with petrol engines to keep the U.L.W. under 3 tons and therefore allowing them to travel at 30MPH instead of 20. When these limits were relaxed in, I believe 1958, they were converted to diesel with Perkins P4 motors. Not that I would have thought happened with Pickfords but such a vehicle could have been driven by someone under the age of 21 at below 3 tons. This was how I started in 1954 on a Morris-Commercial.