It was a joint operation with MI6 and CIA. It was British oil interest specifically that stood to gain, but attacking countries who try to nationalize their own national resources always has vigorous if not direct US support.

Also at the time, the "Imperial core" had shifted from GB to the USA since WW2. There is a ton of financial power in London to this day, and certainly back then. But the question of which nation was acting on behalf of domestic national interests and which nation was acting on behalf of international imperialist interests, even though there is often a lot of over lap such as in this case, is another very important dynamic to consider. In 1956 that was really the start of the US as an imperialist player, the Iranian coup is known as "The CIA'S first coup".

Its really sort of an interesting time, an interregnum, where that imperial power was moving from one base to another, and the question of who was really in charge was fluid and developing in part because of this event.

But one way to determine it would be to see who was actually in charge of operation TPAJAX, and that was Kermit Roosevelt, grandson of ex president Teddy R.

The 1956 Iranian coup and learning about the US's role, was one of the things that radicalized me and turned me into an anti-imperialist and socialist, as a young man with little education or prior interest in politics.

But that wouldnt be true.

It may have started to protect british interest, but those were also in Americas interests as well and the Americans did the lions share of the dirty work.

Obviously im not saying Britain is without blame here, but to make the obligatory Nazi comparison its like saying all the axis nations were as bad as Germany.