Libya is no more a case for or against carriers than the Falklands War forever proved their worth. The fact that we did have carriers in 1982 meant that having mis-judged the political situation in the Argentine (Lord Carrington resigned) we were then unable to protect British interests.
Along with other military assets, our carriers allowed Mrs T to have some chance of re-taking the Islands by force if necessary, without unacceptable risk and great loss of life. In deciding to do so, she saved her reputation and that of her Government and many of us around at the time would say, of the UK as a whole. Mrs T could just have accepted what had happened and brought the Islanders home. An interesting point given that later that decade, the Hong Kong issue was solved by giving China what it wanted and stripping residents of many of their rights to British citizenship.
So you are correct. If we are skint, do we really need to provide for anything other than homeland defence? I think with Libya and the two dozen plus conflicts we have become involved with since World War Two, you have a clue to the answer. HMG believes that our interests are global in nature and our Armed Forces' must reflect the need to defend against potential threats to them. That's why the carrier(s) F-35, AAR Tanker's etc survived SDSR. Recent events simply bring into focus the assumptions made for the pre 2020 period that allowed the more immediate cut backs in certain capabilities.
When we help to bail out Portugal as was also the case with Ireland, it will be to protect British interests and the money will be found
