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Tactical2017 said to vote LD there
It's easy to say this with hindsight but tactical2017 gave too much weighting to the remain vote per constituency (which would bias their suggestion towards LibDem rather than Labour). This is something I'm sure they'll take into account of their next suggestions if there's another election soon.
In the vast majority of constituencies (of the 632 in GB) their suggestion won or came second behind the Tories.
But there were 58 constituencies where they suggested a LibDem vote that ended up coming 3rd (and so another non-Tory party was second or won). I haven't looked at these in detail but I'm guessing that these were high remain areas where they thought the voters would be shift to LibDem based on their intent to remain rather than Labour's commitment to continue with Brexit.
(Again I'll repeat that the data show that their suggestions never split the vote to prevent another party winning. In these 58 constituencies the votes for the tactical2017 recommendation would not have helped the other party overcome the Tory majority.)
To me, there should be no recommendation for tactical vote in seats which are absolutely safe eg Sutton and Cheam. Tactical2017 said to vote LD there, because recent history says they have support there. But the result gave yet another big shift from LD to Labour, providing a counter for the "Labour can't win here" rhetoric that LD campaign on. now 2022 or whenever might see a stronger turnout from traditional Labour supporters here.