Recent quotes:

Tactical voting to beat the Tories: does the maths equal a coalition? | Science | The Guardian

At present, the Tories look set to win about 392 seats with Labour crashing to the Hagueish total of 170. A perfectly-executed Lab/Lib pact could reduce that to about 361, handing 25 seats to Labour and 6 to the Lib Dems. If all progressive voters were directed by an all-seeing omnipotent god-being to perfectly optimize their vote then the Tories would land in the 330s. That would still leave them over 100 ahead of Labour (on 217) and be enough to form a majority. In summary: even if a progressive coalition made any sort of political sense in a reality where Tim Farron and Nicola Sturgeon would have to prop up a guy who can’t even claim a majority of his own MPs; it would require a polling error unlike anything we’ve ever seen combined with literally an act of God for it to work.