Yesterday I reported that 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.

The Huffington Post reports that House of Lords could be controversially suspended or “flooded with Tory peers” if it takes the “nuclear option” of killing off George Osborne’s tax credits cuts next week, according to government sources. This is a truly remarkable threat from the Conservative government, in a so-called first world liberal democracy.

Furious Conservatives are threatening the unprecedented and profoundly undemocratic retaliation if peers decide to proceed with the step of using the so-called “fatal motion” to kill the Chancellor’s plans to cut working tax credits.

Campaigners believe that the usual Salisbury convention, which stops the Lords from blocking a party’s plans, does not apply because the tax credits cuts were not mentioned in the Tory manifesto in May.

But a fatal motion on what the Tories deem “a financial matter” would be unprecedented and Tory sources say the government are determined that the Lords would “have to pay a serious political price” if the Government is defeated next week.

Normally if the Lords defeat the Government on a money-related bill, it can be overturned easily in the Commons by the Speaker deeming it a financial issue. But a statutory instrument has no such condition.

Baroness Meacher told BBC Radio 4’s World at One on Monday afternoon that the cross-party determination to overturn the plans was strong.

Asked how much support she had, Meacher said: “A lot. There are clearly a lot of Conservatives who are very worried about this. There’s very strong support from the Labour Party and Lib Dem, cross-benchers who are very worried.”

And the government’s threat comes when several Conservatives have warned the tax credit cut will be damaging. Also speaking to the BBC today, even Boris Johnson ramped up the pressure on the chancellor. The London mayor said while it was “brave” and “right” to reform the tax credit system the government needed to make sure it was done in a fair way. He said:

I think everybody is concerned about everything that bares down unfairly on the working poor and it’s very important as we take this thing forward we do it in such a way as to minimize that impact.

Baroness added that Bishops in the Lords were “very deeply concerned” and would “want to support a rethink” of Osborne’s plan. Asked if the Bishops would support her, she said: “That’s my understanding.”

This is an unprecedented and extremely undemocratic threat on the part of the government. The House of Lords shares responsibility for making laws with the House of Common. The role of the House of Lords (sometimes called the “upper house”) is to provide an additional safeguarding mechanism of democracy, as the second chamber of Parliament. Members regularly review and amend Bills from the Commons.

The House of Lords plays a vital role in making and shaping our laws and crucially, in checking and challenging the government; it shares this role with the House of Commons. The Lords has a reputation for thorough and detailed scrutiny of Bills.

The House of Lords serves a valuable democratic function by providing a national forum of debate free from the constraints of party discipline. Although the defeat of government legislation by the house has been relatively rare on major legislation, it sometimes does defy the government. Members come from many walks of life and bring experience and knowledge from a wide range of occupations. Members use their extensive individual experience to investigate and scrutinise public policy.

Much of this work is done in select committees – small groups appointed to consider specific policy areas. Members play a crucial role in holding the government to account.

In late 2011 and early 2012, the Tory-led Coalition government suffered a series of defeats in the House of Lords on amendments to its flagship Welfare Reform Bill. Most of the defeats were on highly controversial matters, including the bedroom tax, disability benefits, the reform of the child maintenance system and the introduction of an overall benefit cap.

The Lords also tabled amendments to the Legal Aid, Sentencing and Punishment of Offenders Bill. All were subsequently overturned by the House of Commons, which cited its “financial privilege” – or the right to dismiss the Lords’ demands on “financial matters”. As a consequence it was argued by the government that the Lords should, by convention, not insist on its proposals.

These events provoked anger both inside and outside parliament, with claims that the government had misused parliamentary procedure in order to secure its extremely controversial policy programme, and that the incident could be considered not only as profoundly undemocratic, but also, as “an abuse of privilege,” and a means of avoiding unwelcome scrutiny of and accountability for objectionable policies. A widespread complaint is that the financial privilege process lacks transparency.

At present there are no clear definitions as to what falls within Commons financial privilege. And once privilege has been invoked on an amendment, the Commons gives no explanation as to why. Such lack of transparency makes it difficult for peers to anticipate whether financial privilege will be applied to their amendments, and has certainly fed perceptions outside parliament that the process is being abused.

There is also a lack of transparency about how the Lords may respond when faced by a claim of Commons financial privilege.