"The (Bell) Airacomet....was made possible by a very notable example of reverse Lease-Lend. Britain sent the original engine used in the Gloster e.28/39 together with full information and data we had obtained, to the American government. This gave America a flying start, of which it does not seem to have taken the fullest advantage..."
Not entirely accurate. The Airacomet's original engine was a licence-built DH Goblin which somehow got wrecked. The engine we sent to replace it was a "real" Goblin removed from the second prototype Vampire. Incidentally, the prototype Meteor also first flew with DH engines as the Whittle/Rover/R-R engines weren't ready.
I'd not heard about balance of power being a reason for supplying Nenes to the USSR. The deal was apparently approved by Sir Stafford Cripps who was deeply religious, highly principled and had massive personal integrity. Unfortunately he hadn't realised that not everybody was like him...