The chances of the government being defeated on plans to cut tax credits in the Lords next week have risen markedly after the Liberal Democrat leader, Tim Farron, instructed his peers to vote for the fatal motion to block them.

The Lib Dem peer Lord Kirkwood had been planning to move a motion of regret, which would have amounted to a request for the government to reconsider its plans.



Tax credits: what are they and who benefits? Read more

But Farron’s intervention on Tuesday means the government is now likely to be defeated, requiring ministers to restart the process in the Commons via a new statutory instrument.



A Lib Dem spokesman said Farron had instructed a heavy whip on his peers to back the fatal motion. Some opposition peers are anxious they may be over-reaching their constitutional powers by challenging a main part of the government’s financial programme.

Opposition peers recognise that they can defeat the government repeatedly and almost at will as long as Lib Dem peers unite with Labour and a few crossbenchers to defeat the Tories.

By custom and practice, the peers do not challenge financial measures, but Farron has been arguing that the specific tax credits measure was not in the Conservative party manifesto and was even specifically denied by David Cameron in a leaders’ TV election debate, after the Guardian revealed a document leaked by the Lib Dems showing that the government had been considering cuts to tax credits.

Farron also believes that Lib Dem peers are free to throw aside constitutional conventions since the government has set its face against reform of the Lords.



George Osborne fended off Conservative MPs anxious at the proposed cuts to tax credits at a private meeting of the party’s 1922 backbench committee on Monday by insisting the changes have to go ahead and warning that if he had not acted, £15bn of spending cuts would have to be found elsewhere.

In a Treasury analysis released to coincide with the backbenchers’ meeting, the government said that without action, spending on tax credits would have risen to £40bn by 2016-17, a £10bn increase from 2010-11 and £15bn lower than now forecast as a result of the cuts introduced by Osborne in the summer budget.

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