Given the cost of the ships and buying a decent number of aircraft to fly off them, I can't think why the Treasury would quiver at the cost of sourcing catapults and arrestor gear abroad. As we need just one (or two in the dream scenario) systems, it must be quicker and cheaper to buy the US equipment being built for the CVN-21 rather than re-invent the wheel?
I seem to recall that MacTaggart Scott's Direct Acting Water Spray arrestor gear was only ever fitted to the previous Ark Royal. That gear was designed for CVA-01 the Fleet Carrier cancelled in 1966.
Carrier Strike has enough risky elements as it is. Adding another with a one off UK order for "cats and traps" is unlikely to be the low cost option! If cost is really an issue though, how about a mixed order for Super Hornets but fewer F-35C's with the former primarily at sea and the latter only deployed for training and then as and when required.
