Chancellor George Osborne has vowed to take on the House of Lords after peers dealt a devastating blow to plans to cut tax credits.
The vote - the first time in 100 years the Lords has defied the elected Commons on a financial matter - saw a motion to delay the £4.4 billion of cuts while an impact assessment is carried out win by 307 votes to 277.
A second motion to delay the cuts by at least three years was also passed, by 289 votes to 272.
Mr Osborne said both he and Prime Minister David Cameron were "clear" that the rebellion would "need to be dealt with".
"It has happened, and now we must address the consequences of that. I said I would listen and that's precisely what I intend to do," he added.
"I believe we can achieve the same goal of reforming tax credits, saving the money we need to save to secure our economy, while at the same time helping in the transition."
A Number 10 spokesman said now that the century-old agreement between the Commons and the Lords had been broken, Mr Cameron had ordered a "rapid review" to try to "see how it can be put back in place".
They are not there to interfere with the settled will of the House of Commons, warned Boris Johnson.
A working mum who would be hit by Tax Credit cuts spoke to ITV News ahead of the House of Lords vote on the changes.
Peers will have to decide whether to delay changes to the tax credits bill, review them or scrap it altogether.