When the RN was forced to withdraw from 'East of Suez' in the early 70s, there were suggestion thrown around that the amphibious ships (LPHs and LPDs) were no longer needed (the Fearless and Intrepid were not even ten years old at the time). The RN responded by grabbing hold of the 'NATO Northern Flank' role and holding on for dear life, also allocating the RM Commando force too, the idea being they would be used in WW3 to reinforce Norway at short notice and were far more efficient way to do this than requisitioned North Sea Car Ferries as some were suggesting.
In 1982, Car Ferries were indeed requisitioned for amphibious transport, but could only act as supplementary transports, not as primary assault ships. The LPDs and LPHs were still needed. Only one LPH was left in service, Hermes, but much to the disappointment of the head of the Commando force, she would not be available to him as she would be busy providing Air Defence and Strike to the fleet... what we really needed was a much bigger ship, large enough to do both jobs at the same time. That's the real Genesis of the QECs, conceptually replacing both Hermes and Bulwark in one hull! People complain they aren't like a Nimitz, well that's not what they were designed for!