Yesterday, I saw a Unimog U1250 at Barrow Hill with no identifying marks except that it had been been for sale by BAS Trucks. Thanks to the powers of Google (and because it was still carrying BAS Trucks' item number), I have found it on the Internet here https://www.bastrucks.com/vehicles/used/truck-flatbed_open-mercedes-unimog_424a_u1250-1987-4x4-70108491 and it even has its own YouTube video here (works plate visible inside the driver's door at 1.20!)

There aren't many U1250 (424A) types in the OTP books and due to the fitments e.g. the type of rail wheels which are one large rather than two small and the lack of an engine vent on the front right side, it's easier to say what it isn't which is any of those pictured in the books or on site. It is still exactly as it was when for sale with a tank and spraying equipment. Of course, with BAS Trucks being based the Netherlands, it may be new to the UK.

Can anyone identify it, please?

This is an import therefore will not appear in the previous OTP books. Certain pictures on the dealers site show a roof mounted road works sign with flashing repeaters, which may be French I believe.

Presume this is a jetter of some sorts

Positioning of jets could suggest clearing tramlines etc

Only a suggestion though

Unimog still at BH today (31/1/20) now facing in the opposite direction. There is a sheet in the window listing BAS Trucks and the number 70108491.