George and everyone interested:
the argos pressure cooker for 14+? is the one I got. It's 7L, but speculatively seems to only operate at 7PSI by default, which is very low judging from this thread and my recent attempts at cooking the 3litre C2G base. I also should assert that in 1h10minutes, at a lower flame, the pressure cooker never hissed. Only when I raised the flame a little did it start hissing, but as I was afraid to burn things, I decided to lower it immediately.