Apparently the best-case scenario is mid-october, although it's from an unnamed source in the Express, so who knows how reliable it is.
Coronavirus vaccine in UK in SIX WEEKS! Best scenario now mid-October
A VACCINE for coronavirus could be ready in just six weeks in a "best-case scenario".
www.express.co.uk
Revealing news of the work on a vaccine, the source said: “We are looking at a best-case scenario of six weeks to develop and test a vaccine – and that would be a game changer.
“Even if it takes longer, we feel Oxford and Imperial are close. Obviously, it then needs to be rolled out and millions of doses given to the public but we have built up the manufacturing capability.”