Incredible Twitter thread here about polling during the 2017 election:
Part 1: https://twitter.com/chriscurtis94/status/1534444485907779584
Part 2: https://twitter.com/chriscurtis94/status/1534448340770906112
The thread alleges a private company, YouGov, was threatened by the UK Government not to publish legally releasable information and forcing said company to manipulate future information to make the Government look better. The source was YouGov's Political Research Manager at the time of that election.
Some key polls that were supressed include Labour drawing level with the Tories on the day of the Manchester Bombings and a leaders' debate poll (I'm guessing after the 29 May Sky/Channel 4 debate) showing one in four Conservative voters thinking Corbyn performed best, with a huge Corbyn win among the general public. Additionally the methodology was adjusted in order to boost the Conservative share in the final polls. All of these things would have been are major psychological moments - showing Labour could win the election, Corbyn was actually popular vs May and Labour had continued momentum going into polling day.
It shows polls could be manipulated by governmental pressure in order to affect public opinion. Also makes me wonder how much influence the government has over major companies.