The Aim
Giving this a bit more thought, there's little point in just enforcing a NFZ, it would need to be in order to achieve something. Stopping the Libyan's bombing and strafing themselves would be a good start but there would be some ROE issues especially as civil air needs to continue for a good while yet. There is little point in threatening to shoot down Libyan military aircraft if they then close down their airspace to all users and deny use of the international airports. We would probably need to offer some protection and cover to civ air where possible. This would be a huge commitment. A likely scenario might be to totally closedown the airspace in the west but maintain some civi air corridors to airfields in the east,
Very soon after, we would need to be able to get in close to provide some kind of recce and attack cover for the population on the ground along the lines of that provided for the Marsh Arabs. Not ideal and not easy but putting troops on the ground would likely be a non-starter. And so the whole thing could escalate.
The term NFZ is very misleading. We should really be talking about something between a favourable air situation and air supremacy and then define what we would do with it. The SAMs would be a continuing issue.
Whatever the operation, I really don't think that a CVS with a few Harriers would have been up to much - so do we really miss them? They would have provided a lot of hot air and bluster on the news but would likely provided very little to the NATO air commander.