Back in 1965 it cost 4d to post a letter and so this denomination was very popular. The Post Office issued a special set of stamps marking the 25th anniversary of the Battle of Britain and there were six different designs for 4d, plus two others for more expensive postings.

The link here also talks about a plan which would have seen the Queen's portrait disappear from our postage stamps, but of course 50 years later she's still on them!

http://www.bbm.org.uk/BattleofBritainStamps1965.htm