Yes, the Silkworm was used in the Falklands, and it would be the greatest threat to shipping. It is very large and effective. They are also rumored to have some old soviet cruise missiles.
I understand that those torpedoes are very recent, and I highly doubt Russia would let anyone have one for a while.
This little guy would not rate a hunter/killer. All you need is a couple of Sea Stallions and a handful of sonobouys, and that thing is history.
Being a diesel/electric makes it quiet, but very short range. It's size would limit its underwater time. It would be nothing but a coffin (IMO).
I thought it was an Exocet missile that sunk the British ship.