The so-called 'shy Tory' effect has been fairly conclusively proven to not actually exist; people will claim to be 'undecided' but will not claim to support X a

The so-called 'shy Tory' effect has been fairly conclusively proven to not actually exist; people will claim to be 'undecided' but will not claim to support X and then vote for Y. Look to size of the undecided group and then see where they break if the pollster forces a decision -- in 2020 the undecideds are smaller, and unlike 2016 they are breaking hard against Trump.