Encyclopedia Astronautica wrote:

There was also a British design for launch atop a Blue Streak-derived
LV which I haven't added to my site yet. As I recall the justification
was given that it was strictly notional, to allow simplified
calculations (as was the case with the F-117 and radio waves).

I've seen that one- it's the one with the cylindrical crew compartment
(that rotates during flight to match the angle at which G forces are
being encountered?) that was designed by Armstrong-Whitworth in 1959
with Nonwieler's help; there are drawings of it on page 423 of Ron
Miller's "The Dream Machines".
It was too use a lightweight & jettisonable "Image Fairing" of
identical shape to the vehicle clamped to it's belly 180 degrees
reversed during ascent- to even out the aerodynamic forces and drag, and
so to cut down on the need for stabilization of the launch vehicle
during atmospheric flight.

Pat