Are you talking about 'predictions' of what would happen with the lockdown or without the lockdown?
In his presentation in the press conference with Boris Johnson on 31st October (see link, below), Vallance made it clear that the 'predictions' (if that's what you want to call them) related to the situation in which changes were not made to the mitigation measures in place. However, changes were made. So to compare those predictions with what is actually happening is, obviously, pretty meaningless.
Two example from the presentation.
1) The slide presented at video time 8:36 has the title "WINTER SCENARIOS FROM EARLY WORKING ANALYSIS: England daily deaths if no changes in policy or behaviour". Note the phrase
if no changes in policy or behaviour.
2) At video time 11:20, Vallance says "So unfortunately that's a very grim picture in terms of what this looks like in the absence of action and continued growth." Note the phrase
in the absence of action.
It's also important to understand what is meant by phrases such as 'reasonable worst case scenario" and "what could happen".
https://www.youtube.com/watch?v=7B1sBUdQeio