Only the left can change first past the post

It is only the political left who are able to change the voting system because it is only they who get elected.

The first-past-the-post system requires of voters on both sides to be loyal to the main party on each flank. For the left this is easy since leftist voters tend to be loyal but for the right this is more of a problem because their voters are not so interested in being loyal to the main party. For them (the right) it is much less of a contradiction to vote for one of the smaller parties. This means that the left generally prevail in a fptp election. Because the left are generally in power when fptp is used it is only they who can change the system. The party of the right could change it if they get into power but they are always excluded because the fptp system favours the (political) left. It is only the left who can change the fptp system and replace it with a system of proportional representation because the right are never in power when fptp is used.