we know that now; but if you look at the paranoia in the admiralty surrounding the pb's versus their relative indifference to the japanese build up, one can certainly get the feeling that they didn't know that then
i don't want to make this into "raid" where the british sit back and do nothing; but the claims of knee jerk mega build up are overstated
britain showed a sensitivity to german shipbuilding in public and private debate... but they didn't actually counter the pocket battleships for all their handringing (and they didn't need to as the ships were largely no more effective than any other cruiser IRL)... there was hardly any thought at all as counter the GZ and no active counter build against her
for the moment, i'm figuring ark royal gets two sisters and the three most useful existing carriers get modernized to the degree possible, thus giving the british 2 modern full fleet carriers for each German light carrier
this gives the british 45,000 more tonnes of carriers vs the germans just going with their otl tonnage so that shouldn't be straying too far into wank territory yes?
Well, the RN probably thought 7 carriers to one carrier prototype reasonable odds re. the GZ....
They would go for a bit more than 2:1, though.
The RN has to assume some carriers might be needed outside the North Sea, plus that there are refits to consider (a German raid wouldn't have any ships in refit).
The only useful older carriers were Glorious and Courageous, so on the basis of carriers I'd expect 3 Ark class, for a start. But remember, there is that big Air Ministry issue with the FAA and available planes, if the Germans have carriers that have to be matched something is going to give in the UK armed forces internal politics, and it could get bloody....