A referendum on changing the voting system for general elections will now take place on May 5 after peers opposed to the Government's bill eventually backed down.
The Parliamentary Voting System and Constituencies Bill received royal assent last night after a torrid passage through the Commons and Lords.
Ministers needed to get the Bill through Parliament before peers began their February half-term recess today in order for preparations to be made to hold the referendum at the same time as elections to the devolved institutions and local councils in England.
Earlier, for the second time in 24 hours, the Commons threw out an amendment by the Lords demanding that any referendum on dumping first-past-the-post elections for AV (alternative vote) should be binding only if there was a turnout of at least 40%.
Deputy Prime Minister Nick CleggThis is a real milestone in restoring trust in our political system and making our democracy fairer
The AV system allows electors to rank candidates in order of preference.
The Bill was first debated in the Commons on September 6 last year.
But its passage through Parliament was held up by a dogged rearguard action from Labour peers, which saw the committee stage in the Lords drag on for 17 days, with late-night and all-night sittings.
Labour wanted to wreck the Bill because it also includes proposals to cut the number of MPs from 650 to 600, and create constituencies with roughly equal numbers of voters.
Voters can choose to ditch the first-past-the-post system
In a sign of how important the legislation was, Lib Dem leader and Deputy Prime Minister Nick Clegg called off an official visit to South America this week to help secure the Bill's passage.
After the Bill became law he said: "This is a real milestone in restoring trust in our political system and making our democracy fairer.
"Constituencies will be redrawn, so that votes are more equal throughout the country.
"And, for the first time, through a referendum, voters will have a say in the system they use to elect their MPs.
"Together, these measures will help put the expenses scandal behind us and start to restore trust in our political institutions."
