You'll basically need a stronger British economy right after WW2, and drastically reduced US arms exportation immediately following, all with the goal of loosening the US vice-grip on NATO, as after the Empire slips away, the UK will need new markets, and sources of resources. Either the US, UK, or Germany is going to be filling that role. Make sure its the UK.
Basically you need to keep the UK aviation industry from the severe atrophy suffered in the 60's
If, say in the waning days of WWII, the liberated European nations formed NATO under British aegis, and factories all across the empire started churning out Enfield rifles, Stens and Bren guns to rearm Europe, along with guaranteed ammunition and logistical support for the weapons (at a very small fee of course), the UK has more resources to put into defense. And naturally they'll want Centurions and Meteors to go along with it.
But whatever you do, you need to keep British military aircraft as a profitable venture for companies in the UK.