What are these assets?
Couldn't Britain do anything about it?
Assets. Operatives that had infiltrated organisations to provide feedback, or had been acquired from within the organisation. People who tell you what's going on, and sometimes get into the position where they can influence decisions. In the case of the IRA assets, the CIA was offering a carrot in an attempt to persuade the IRA not to target US interests in Ireland. Since the IRA didn't target US interests in Ireland, that has to count as a success. It didn't even cost the CIA anything.
Re Turkish invasion: ever since Suez, British foreign policy has, to all intents and purposes, been in lock-step with American. In 1974, Britain was about to ensure an RN presence to prevent the Turkish invasion. Kissinger wrote to Callaghan (Foreign Sec at the time, IIRC), basically saying: "Don't. Or else." So Britain didn't. Britain took the attitude that provided the British bases on the island remained secure, their interests would be OK. Kissinger took the attitude that he needed to be nice to Turkey, and Britain would do whatever he told them. Given the state of the British economy at the time, he was probably correct. The Kissinger-Callaghan letter is an interesting little snippet in Anglo-US relations of the period.
