I think somebody is getting paranoid. Why is Whitehall using this policy to keep Manchester in its box?
The policy could be seen as being equally as detrimental to Stansted, Gatwick, Birmingham, Edinburgh etc
Singapore already does flights beyond Manchester, and Biman Bangladesh used too. In recent years, Air India used to transit through Birmingham to Toronto.
Ethiopian also use Dublin for US pre-clearance which is something that cannot be done using a UK airport.