There are 29 minor party and independent MPs in the newly elected House of Commons. The 5 Sinn Fein MPs can be discounted because they never take up their seats. That leaves 24. Hence, a grand coalition of all parties bar the Tories – very unrealistic because of the large number of different players involved – would only be able to muster 339 votes, a paltry majority of 14.
Such a majority would not sustain the coalition for long if at all, because (1) there would inevitably be regular rogue votes against coalition policy by members of the coalition because of the number of different parties involved and their disparate ends and (2) any Parliament suffers a gradual erosion of the general election personnel through death, serious illness and resignations for other reasons.
There would also be the complication for the Celtic Regional Parties (especially those in Ulster) of being constantly on call for votes when they are (1) a long way from London and (2) some are members of both their regional assemblies and the Commons.
The Tories having almost all their seats in England would find it much easier to maintain a full presence and could stuff the coalition by refusing pairs. RH