The ship on the stamp is identified by Mr. Peter Crichton as one of the Leopard class. He wrote she has a very distinct profile with the very large anti-aircraft radar.
I have compared photo's with the stamp and Peter is correct she is one of the Leopard class, there were four of this class, and only the LYNX I could not find that she has made a call at Tristan da Cunha, the JAGUAR made a call outside the timeframe. The PUMA and LEOPARD made both a call in 1962 during the volcanic eruption, so we have two ships which can be depict on the stamp, most probably the LEOPARD is depict see http://royalnavymemories.co.uk/hms-leop ... ommission/ the beach on the stamp looks very similar as on the photo on this web-site (Hicks Beach).
But we can not be sure so I will give her as one of the LEOPARD class most probably the HMS LEOPARD.