Lets suppose for a moment that the defence cuts don't shut down the RAuxAF flying squadrons. It's aircraft by the mid 50's badly need replacing. Which would be the most realistic aircraft to equip them with?
Personally I think the Folland Gnat would be a good candidate.
I think that the F1 Gnat would certainly fit the role.
Although it is worth noting that while cheap to make and operate it did require considerable servicing on the ground relative to similar aircraft types - this mainly due to its compact nature making access to some components difficult - also early versions had unreliable Hydraulic and control systems.
However if perhaps the RAuxAF aircraft leveraged the work done on the T1 Trainer and subsequent changes along the lines made to the Indian HAL Ajeet version (built in the 70s) then some of these issues may be resolved over the life time of the Aircraft in RAuxAF service
Also it (The Ajeet) proved to be a capable fighter in service with the IAF more than holding its own vs the PAF F86 Sabres (considered by many to be the best dog fighting jet) in combat
An improved F1 fit for purpose would not likely be 'realistically' available until the early 60s
If it continued service into the 70s/80s then it might be upgraded to an F2 variant with Sidewinder missiles etc although the obvious thing would be to replace it with the Hawk
Would the 20 Squadrons all be light fighter or would some be re-rolled to other AC types - ie Helicopter / transport aircraft squadrons?