According to the seller it's a Boosey & Hawkes (Class A). As you can see it's not a compensator but I'm still going to check it out in a couple of hours.
The large top bow having ferrules directly on both sides of the semi-circle rather points towards France than towards the UK in my eyes.
This is not at all a derogative. This tuba looks like having quite large outer branches with potentials for a full sound. It will be interesting to hear about its intonation.
The valves of that one where very leaky . It was not even worth it to take it home as a project. There was also an other Tuba for sale. This one:
The valves of this one are in very good shape. They are smooth and very tight. Corks and springs need to be renewed but the tuba played very responsively. Unfortunately it is high pitched. Nevertheless took it home and I’m going to have it converted to low pitch.
The serial is #105957 and the bell in engraved with:
Class A
Besson & Co
"Prototype"
London
England