In the internal report Refounding Labour op.cit. there is a clear acknowledgement that the two horse race (which made first past the post defendable) no longer applies. At least some in the Labour Party understand even if they are not willing to embrace the implications.
"General elections used to be a two horse race. No longer. In the 1950s and 1960s Labour and the Tories regularly took 90 per cent of the poll - fully 97 per cent in 1951. That dropped to 75 per cent in the mid 1970s. And it has dropped at each of the past four general elections, reaching a new low last year of only 67 per cent. This is the lowest level since 1922 when Labour first emerged as the main opposition to the Tories"
From the Introduction by Peter Hain