There is a consistent majority for liberal (progressive) parties in the UK, but they regularly cannibalise each other in the first-past-the-post voting system (see Wikipedia for details). The last four UK elections were won by the Conservatives yet in three of them the three principal liberal parties (Labour, Lib Dems, Greens) had more votes than the three principal conservative parties (Conservatives, UKIP, Brexit). So it would seem that proportional representation (PR) would lead to a higher probability of Labour-led (coalition) governments.
Yet while there is a campaign group in the party, PR does not seem to be a commonly accepted position. Why is that?
Does Labour prefer to win less elections but then govern without a coalition, or
does Labour hope to eventually absorb the (older) Liberal Democrats and the Greens?