As long as they do things that the Lib Dems, SNP, Plaid, Greens and long tail of "left/progressive" candidates agree with then they have the support of a majori

As long as they do things that the Lib Dems, SNP, Plaid, Greens and long tail of "left/progressive" candidates agree with then they have the support of a majority of votes (they only need Lib-Dem and Green for over 50%) and will get an overwhelming number of MPs supporting their motions. They don't need to do that, due to the flawed system, but it seems likely in most cases.