Reading an old paper - 'The Case for an Electoral Pact by Labour and the Liberal Democrats' by Martin Dent, Political Quarterly, 1993. He proposed that the parties stand down their candidates in marginal seats but only where their support didn't muster 15%. Categories of seats:-
A bit 'pie in the sky' and given what happened after 1993 superfluous however Dent was an interesting character:-
I remember seeing the report of the redrawing of constituencies in Wolverhampton Library once, magnificent hand coloured maps with detailed descriptions of who owned what and the suffrage prior to the great reform act.