Per Ogorkiewicz, the final Armstrong-Siddeley tank engine was an aircooled 180 hp V8 used in the Vickers Mark III and the A7, which doesn't appear to be linked to any known aircraft engine of that company. That effort allegedly ceased due to lack of funding.
Without going into the debate of aircooled vs liquid cooled tank engines and without knowing about the alleged technical issues this engine faced in both tanks, I'd argue there would still have been merit in continuing the Army-AS cooperation to obtain a more dedicated tank engine manufacturer and possibly more suitable engine designs. Moving to a V12 alone would yield 270 hp by the mid 30s, and it surely was possible to improve or extrapolate the AS Vee engine to obtain something more modern than the Liberty and more suitable than all the truck engine derivatives (Inline or flat).
Considering that a bunch of companies like Rover and Meadows eventually built Meteors and that Leyland had come very close to producing it before chickening out over the technical risks, I still believe that as long as the British govt paid, they could have set up production of any modified aircraft engine before the war no matter what the Air Ministry said. At the end of the day, the problem really was that the govt prioritized aviation needs to a very high degree over the Army's. I won't go into whether that was the only possible path.