Well it all seems to slotting together now.
@StrawberryRipple and
@knome posted the articles about the little publicised change to the law changing the end date to 17 July.
Today I read an article where the head of AstraZeneca (I think it was) said that the vaccine supply would stabilise when the UK had vaccinated 75% of the population enabling herd immunity, probably around the 14 July.
It's like watching a jigsaw puzzle being slowly completed, but we don't have the picture on the box to go by.......................