Alex Salmond's dramatic move - after a night of drama in Scotland and a day of confusion in Westminster - adds another variable to the outcome of the constitutional crisis.
The result of Scotland's independence referendum electrified the UK - and the ramifications of the no vote have spread across the world.
The Conservative party now firmly believes Scots MPs should not vote on English laws - which could make it much harder for Labour to form a future government.
Constitutional reform proposals are flooding out of No. 10 (without much consultation it seems) in the wake of the Scottish referendum. So is now the time for much needed House of Lords reform?
Commons leader William Hague tells Channel 4 News the constitution needs to be rebalanced to give English votes to English MPs.
Alex Salmond announces his resignation as Scotland's first minister and SNP leader after failing to achieve a yes vote in the independence referendum.