1918 general election

What would be the best means to ensure that the small but notable upsurge of minor parties in the 1918 election go on to play a major role in the interwar period? Parties like the "patriotic labour" National Democratic and Labour Party, the far-right National Party, the patriotic-Marxist...

As it says on the tin: Keep the entirety of the island of Ireland part of the United Kingdom with a Point of Divergence no earlier than December the 15th 1918 (the day after the 1918 General Election).