Why the Avro York considered Merlin and Hercules engines

Why were both Rolls-Royce Merlin 22 and Bristol Hercules VI engines considered for the Avro York?

The preferred engine depended on availability, competing demand and whether enough units could be produced.

The choice was not simply a contest over which engine offered the best paper performance. British planners also had to ask which type was available, which had fewer competing claims and whether production could supply enough units. Considering the Rolls-Royce Merlin 22 and Bristol Hercules VI therefore preserved flexibility across two engine families while wartime demand shifted. Aircraft design in this case depended on production allocation as well as engineering preference.