Given that the EM-2 had been announced as the next service rifle by the outgoing Labour government and the War Office went so far as to give it a proper name (Rifle No 9, Mk 1) it indeed seems that there was an actual intent to issue it as the general service rifle, along with the Taden gun. Churchill killed it but only cos the twats in the US Army were committed to .30-06 for reasons of economy and/or sentiment. Certainly there was no science involved.
Still, the US was at the peak of its game at the time, engineering moderately improved Garand derivatives and eventually the ultimate peak of weapon's design, the M-60 GPMG.