Obama would be the first major presidential candidate to drop out of the modern campaign financing system for the general election since its creation in 1976 in the post-Watergate era.

CNN: McCain attacks Obama for opting out of public financing

On Wednesday Mr Brown set out some of his intentions for constitutional reform - which included looking at whether Britain should change the first-past-the-post electoral system and reforming the House of Lords - both of which would be unlikely to change before next election.

BBC: Brown holds 'next steps' meeting

If that second election transpires, it looks increasingly likely to be held under the same first-past-the-post voting system that Westminster has always known.

ECONOMIST: Election results