The Hellenic navy's submarines were of french design, so perhaps they also had french torpedoes (of which data is hard to obtain)? Do you have any sources for the claim of british torpedoes being used (and in particular the two specific models you mention)?
There are several british torpedoes with speed as low as 30 kn though.

The torpedo in your last link looks very much like a Sovjet Type 53-38 torpedo (speed-settings: 30,5 / 34,5 / 44,5 kn). Hard to be 100% sure from the photo, as the design is very similar to Italian contemporary designs.