Good tiemline Ming, keep on the good work !
Consider the following elements
Avro Arrow for the RAF
According to Tony Buttler, the RAF really considered the Arrow as an interceptor, circa 1956.
The RAF problem was to find a successor to the Gloster Javelin. Enlarged, moire powerfull Javelin were pushed by Gloster - called P.356 to P. 376, the latter a monster with a couple of powerful Olympus engines and a so called thin-wing.
The Javelin, however, had a very serious drag problem: even with a thin wing and two Olympus it was barely supersonic.
That's why the RAF started the F-155T spec, which produced monstruous designs such as the Armstrong Withworth AW-169, the Fairey Delta III, Saro 187, Vickers 559... incredible brute-looking machines !
Buttler clearly states the Arrow was no match for F-155T, but the RAF still considered it to fill the gap and replace the Javelin.
The F-155T, however, was far beyond GB finances of the time, and fell victim to Britain own Diefenbacker, namely Duncan Sandys !
So perhaps they could buy some Arrows to replace the Javelin, but not before 1962 at best.
Arrow potential evolution
I don't know if in your TL the F-108 Rapier is cancelled or not in September 1959.
That interceptor very powerful radar and missiles (AN/ASG-18 and AIM-47 Falcon) ended on a B-58 testbed, then on the YF-12.
I'd like to see an Arrow replacing that B-58 as testbed for that very powerful radar and missiles.
Then, when in 1967 the Mig-25 would be seen at that Domodedovo airshow, the Arrow would be the only interceptor able to shoot it.
Israeli and Iranian Phantoms could not shot Mig-25, that's why they bought Tomcat and Eagle in the late 70's.
Perhaps they could buy CF-105 right from 1969 ?