The groom looks out of the loaded horsebox which have been added as tail traffic.
They are of LNER & BR designs
In fact the LNER produced two designs of horse box - for different applications - in 1936-38: one for normal use, the other, with a lavatory for the groom, for the race traffic.

BR built a near copy of the latter in 1954-55 and, two years later, a completely new design (Mk.1) with the race traffic in mind, which was virtually the only traffic left by then and which it was losing.

The photo shows the LNER normal design and BR's second one.