Yes, it may strike some of us as odd: that the Brits would go to the lengths of modifying aircraft carrier hulls, but as Bombhead says, they had the choice of several incomplete classes Centaur/Majestic/Colossus. It goes back to the fact that they had no really suitable cruiser hulls into which to place the projected Seaslug system.
Paraphrasing the blessed Freidman again: the volume available in a Tiger by removing the after 6-in turret and magazine would be just under one-third of that used in the American ships Boston and Canberra for missile magazines alone; the US magazines could accomodate 72 Terriers, the Tiger would be limited to about 20 such weapons, in a magazine which would moreover, extend above deck. And Seaslug, designed for horizontal stowage, would not even fit.
The root of the problem can be traced back to the Washington treaty, and the decision taken by Gt Britain to continue building smaller cruisers (compared to other navies) as these would add the numbers, and also avoiding designing all-new ships. The U.S. started with the Brooklyn's and moved progessively through the Cleveland, Baltimore, Des Moines, Worcester
classes; with the Des Moines probably being the best ever gun cruiser ever built.
The R.N. only had the old Counties with hulls suitable - all worn out postwar. The answer would have been an earlier (wartime) all-new design, with either multiple 6-in or twin 8-in mounts, on a hull well in excess of the Counties. This would make a very interesting project for somone here, and I'll glady adapt it postwar to take Seaslug. And another problem was that the British ships all suffered poor electrical generating - one reason why non of the Battleships could have been converted into missile ships.
of course, what we have here is a flight of fancy, though a lot less that some we see. Given the funds there could have been carriers converted into missile ships. Colombamike has kindly sent me a scan of the alternative Majestic conversion, which I'll add here later. And I'd forgotten that Hood had already visited this project earlier, with the projected Centaur conversion: