The Argentinians not having the capability to buy (or get as a present) the data from the Chinese, Russians or anyone else who keeps an eye on them from space.
If the Russians could spot submerged nuclear subs from a satellite, we'd have bigger problems than Argentina to worry about. But they can't. They can tell how many boats are in port (as can a tourist with a pair of binoculars), and that's about it.
At least at one point this year there was not - the Admiralty unintentionally leaked the fact by stating which one is in for repairs and which one is participating in various junkets (all away from there).
There are three commissioned RN nuclear hunter-killer submarines, with three more under construction in Barrow, and a seventh planned.
The problem with the Falklands in 1982 was that there was only a token military presence (a couple of dozen Royal Marines) and no way to reinforce by air (the runway being relatively short), allowing the Junta to calculate that they could quickly occupy the islands with minimal risk of casualties on either side. This is no longer the case.