[MR4D]

I think there is a finer point to be made here.

For instance, the CIA couldn't care less about BP. Now, MI6 surely did. Rather, the CIA influenced action against Mossadegh because it thought he was a Communist.

Whether MI5 convinced the CIA that he was a communist threat is the more critical question. Some have thought that MI5 simply convinced the CIA of such a story to take out their own bogeyman while keeping their hands clean. It certainly wouldn't be the first time.

Of course, whether or not he actually was one is less notable than his association and support for those who were, as well as his nationalization of the oilfields (technically not the nationalization of BP, but close enough).