Both were designed with the "four plank" hull which gave something between multi-chine and clinker built boat. Each had an early lifting keel, which raised more or less vertically and had a bulb at the lower end, a seaworthy design which was able to explore shallow creeks and rivers.
One of the better known yachts of the type and era was the Debutante, with the less well known sister ship the Escapade, both were designed by Robert Tucker and built by Blanks Boatyard in Hertfordshire. Although very similar in hull form the Debutante at 21' was a bilge keel sloop, whereas the larger Escapade at 25'9" sported a fin keel and double head sail cutter rig.
In 1964 you could buy a Debutante for £650.
I have never seen one, but this Robert Tucker designed Mystic looks like a very practical and sweet design. The raised coach roof is a good way to create interior volume on a small yacht and does so without the reverse sheer which was popular at the time, but which to some people can look unsightly.
Also from Robert Tucker was the 18'6" Caprice, built by "Nobby" Clark of Cowes, one example "Shrimpy" was famously sailed around the world by Shane Acton. Although generally regarded as a bilge keel cruiser, the Caprice was offered in fin keel form as a JOG (Junior Offshore Group) racer with a larger sail plan.
I admit to a fondness for the Caprice, which was the first yacht I owned. Although mine was a late model Mk V built in fiberglass, you still had to open the fore hatch in order to use the toilet.
You can still find examples of these plywood classics, this is an Escapade getting a coat of antifoul before the summer season last year.
This sloop has the look of an early Robert Tucker Caprice, but is sadly looking a little neglected.