Prime Minister David Cameron suffered a setback today when his Lib Dem allies derailed plans for new constituency boundaries which would benefit the Tories.
Lib Dems joined with Labour MPs and a few dissident Tories to ensure that proposed boundary changes will be postponed until at least 2018.
A deafening roar arose from the Labour benches as MPs backed a key Lords amendment by 334 votes to 292.
Indignant right-wing Tory Peter Bone turned his wrath on the Lib Dems, demanding that they should all cross the floor of the House and join the opposition benches.
Experts estimated that the changes would have given the Tories an extra 20 seats.
Proposals to cut the number of constituencies by 50 to 600 were originally supported by Lib Dems, but party leader Nick Clegg threw a wobbly after Tory MPs scuppered his botched scheme to "reform" the House of Lords.