Boosey and Hawkes, besides buying lots of stencils, made some saxophones themselves ( very old ones, prior to yours), but for the most part were stencils based on models sold under their makers names(with a few adaptations just to make them a bit different) .
This one appears to be very similar to a Kohlert Winnenden made in the ’50 or thereabouts. ( those Winnenden horns had much variation of the Spatulas and the Low keys key guard along with the neck brace).
It has soem “ adaptations” to make ik just look a little different but I am quite sure it is a Winnenden.
They are very good horns but they are not very valuable, probably in this state, if playing they would be at most €1000 to a top of €1500 ( if sold by a shop with a fresh overhaul)