I believe the best 2019 GE result we can hope for is Labour the largest party, but so far short of a majority that it will need both the LibDems and SNP to cooperate to put it into power. Forces Corbyn to rein in his extreme plans while taking the toxic Tories out of the picture.
Any seat won by the LibDems helps towards this. But any seat that couldn't be won by the LibDems when seen through the cold analytical prism of reality, but where a tactical voting drive pushed votes to the LibDems regardless, actively hinders the overall "best case" scenario.
In other words, "LibDems everywhere" is a foolish strategy, not an optimum one. Even for those who are passionately Remain. But "LibDems everywhere they have a real chance" is an excellent strategy.
Remember, with the best will in the world, only a small minority vote tactically. So any strategy that begins "If we could persuade all of group X to do Y" is doomed to fail. Be ambitious, but also realistic.
Because the worst result is we're left with a Tory majority and a demonstrable "LibDem effect" i.e. the vote pattern *proves* that the LibDems denied Labour seats in areas it couldn't win itself, because of poor tactical voting advice.
That goes for Labour too. The LD are likely to see a positive effect if the GE turns into the "Brexit election", something that will only become clear after campaigning get under way. And Labour will see a negative effect. That in turn changes tactical voting strategies.
If the campaign ends up more like the one in 2017, where Brexit was an issue but not *the* issue, then Labour may confound the polls (though I still believe they have no chance of an overall majority). But if it's Brexit 24/7 then they're going to suffer.
Summary: if your "tactical advice" consists of "always vote for party X", that's not tactical, that's wish fulfilment. That applies regardless of your own political affiliation. The UK is diverse. There's no "one size fits all" answer when it comes to applying tactics.
