Britain’s first-past-the-post system, in which voters elect a local representative, can sometimes produce unexpected results: Small parties can sometimes fall by the wayside while larger parties receive a majority with only a plurality of the vote.
The below chart shows what the House of Commons might have looked under proportional representation—if the percentage of votes for a political party nationally translated to the same percentage of seats for that party. This system would force the two largest parties to seek coalitions or confidence-and-supply deals with smaller parties. While the Tories and the Brexit Party together could not form a majority under this model, a coalition of the SNP, Labour, the Green Party and the Lib Dems would just exceed the 325 seats needed to form a majority government.
It’s also worth remembering that many voters currently don’t pick their first choice of party at the polls. The first-past-the-post system encourages people to opt for the largest parties, or risk not being represented at all. Proportional representation would favor smaller parties, and might result in voters backing overlooked parties that might actually better represent their views.