UK polling has had a very bad run of late, they got the Scottish referendum, the last General Election, and now the Brexit votes very wrong.
As for the US, IIRC the polls have been closer, and final polls a day or so before and election have generally close to the mark, but with some significant failures as well.
Polling in June is only useful in identifying and tracking trends as the campaign heats up. It is less than useful for projecting winners and losers in a close election.
I would lie to a pollster just for the sheer principle.