Jeremy Corbyn challenges David Cameron over tax credit cuts and affordable housing in his second Prime Minister’s Questions appearance.

According to reports, a rarely-used procedure called a “fatal motion” is set to be tabled in the House of Lords this week, followed by a vote next week, with the specific design of preventing George Osborne from putting his controversial proposed £4bn tax credit cuts into law. In the House of Lords, Peers may table a “prayer” against a negative Statutory Instrument. Under the standard negative procedure, the Statutory Instrument is annulled if the prayer motion is agreed by the House within 40 days of the Statutory Instrument being laid.

Fatal motions are extremely rare, with only a very small number successfully passed since the 1960s, as Peers are wary of overreaching their usual delaying powers with such a drastic “nuclear option.”

But campaigners and crossbench, Labour and Liberal Democrat Peers point out that the fact that the tax credit cuts were not in the Conservative manifesto means they are not bound by the usual Salisbury convention that prevents the Lords from blocking election promises. Opposition parties believe that any move to halt the legislation would be constitutional because the tax credits cuts were not in the Tory manifesto in May, and David Cameron even told TV viewers in the election campaign that tax credit rates would not be cut.

The tax credit cuts were not included in the Finance Bill, which normally enacts a Budget, and the opposition have used the opportunity to seize on the fact that a Statutory Instrument can be halted by a single House of Lords vote.

The tax credit cuts are due to come into force in April, but the statutory instrument needed to make them law is due to be voted on in the House of Lords on October 26.

As I reported in  Welfare Weekly  (and here) earlier, Shadow Chancellor John McDonnell pledged today that his party would reverse the tax credits cuts once it came into power.

The Huffington Post reports that a crossbench peer is being lined up to table the motion in a bid to garner as much support as possible and use the in-built anti-Tory majority in the Lords to stop the Chancellor from going ahead.

The Conservatives have a small overall Commons working majority of 16, however, they are outnumbered in the Lords, with 246 peers compared with 209 for Labour and 106 for the Liberal Democrats. There are also a further 175 peers are crossbenchers (not aligned to any party) and 25 of these are bishops. It is understood that the bishops may also take the rare step of voting against the Government.

The so-called Tax Credits Regulations 2015 (Income Thresholds and Determination of Rates) (Amendment) are in the name of Treasury minister and former Goldman Sachs banker Lord O’Neill of Gatley.

The Liberal Democrats have already tabled a “regret” motion that can only delay the Bill, however, a senior crossbencher will be asked this week table a much the much more drastic fatal motion to kill the secondary legislation.

Among the crossbench names mentioned by campaigners are former social work specialist Baroness Meacher, who has led previous Government defeats on welfare legislation.

Labour also has its own Opposition day debate on Tuesday, which although lacking any binding vote will be used to gauge how many Conservative MPs are worried about the plans, and to court their support in opposing the Bill.

Labour MP Frank Field said:

“This [motion] will be one of those amendments which are rarely tabled but which will kill the measure.

“As time goes on, more of Osborne’s backbenchers are now understanding that far from protecting strivers as the Chancellor promised, he is aiming the biggest cut ever in welfare on this group, who he courted during the election.

“It smashes his 2020 election campaign which would have been all about the strivers. Tory MPs have taken seriously, as the leadership haven’t, that they wish to represent strivers.”

Despite significant pressure from some Tory MPs in marginal seats, the Prime Minister and Mr Osborne have so far rejected warnings that the tax credits cuts will leave large numbers of the low paid workers hundreds of pounds worse off.