Hi John,
It appears from looking at the entry for Sept. Q. 1949 that the birth was missed from the GRO index for that quarter. At the bottom of the page where it should have been, it says "Michael R Westcott see D. 50" This is Dec 1950 which is obviously when it was actually registered because it was missed off 1949 Sept. quarter. So no need to get more certificates!! Anyway that's my theory.
Sally