The Scout seems to have replaced the 14W twin-channel version
of the Westminster in 1962 or 1963. The changes between the two models
were a cosmetic make-over in a larger black and cream cabinet, together with a
different chassis layout (seemingly identical to later versions of the V-front
Dominator, though rated 3W less). The Westminster 10W single-channel model
remained in the catalogue alongside the Scout, but the Scout was a relatively
short-lived model which became the Custom 15 (link) circa 1964/5, hence they are
rare today.
The Scout falls into the period when Watkins were changing into Wem. Some have
brass Watkins logos, some have the later "day-glo" orange Wem logo,
and there are unconfirmed sightings of early versions in turquoise & cream.