The LibDem/Green/PC pact should hold & even expand remain held seats in Wales.
In SW England + London the pact should deliver further marginals to the LibDems as Greens stand down in return for a free run at Green targets.
While the SNP aren’t part of the pact it’s likely that SNP will gain seats from Scot Tories as the party’s purpose as one nation unionists comes unstuck in the face of an increasingly English nationalist Tory party.
In N Ireland non aggression pacts by Sinn Fein (or potential temporary stand downs) could see alliance or SDLP gains.
These areas Scotland, Wales, SWeng, London & N Ire could with pacts easily deliver upwards of 40 new seats from Leave to remain parties.
This is before one even factors in tactical voting.