Ministers are braced for a new Commons battle over controversial plans for secret court hearings in sensitive national security cases.
Labour will seek today to reinsert a series of safeguards into the Justice and Security Bill intended to ensure such "closed material procedure" hearings (CMPs) are used only as a last resort.
Ministers however warn that the opposition amendments would effectively wreck the legislation, making it impossible to operate.
The Government last night received support from former Lord Chief Justice Lord Woolf, who said changes tabled by Cabinet minister Kenneth Clarke would ensure the operation of CMPs was under the "complete control" of the judge in the case.
In a letter to The Times, he wrote: "The Bill now ensures that we will retain our standards of general justice, while also putting an end to the blindfolding of judges in this small number of cases."
That is unlikely to satisfy critics – including some Conservatives and Liberal Democrats – who believe CMPs undermine the principle of open justice and allow the security services to cover up involvement in abuse and torture.
Ministers, however, insist the measures are essential to enable sensitive intelligence material to be introduced in a small number of civil cases where the state is being sued.
The alternative, they say, is that the Government will be unable defend the action and could be forced to pay out millions in compensation – as happened with a series of former Guantanamo Bay detainees.
For Labour, shadow justice secretary Sadiq Khan was highly critical of the way the Government had handled the issue.
The amendments Labour is trying to reinstate were originally passed in the House of Lords, only to be reversed by the Government in the Commons committee going through the Bill line-by-line.
"The Government's own independent reviewer on counter-terrorism legislation says there are a small number of cases where it's worth having proper checks and balances in place so we can have closed material procedures," Mr Khan told Sky News's Murnaghan programme yesterday.
"The House of Lords – crossbenchers, Labour, Liberal Democrat peers – vote to put in safeguards. This Government, secretly upstairs in the committee corridors of the House of Commons, removes the safeguards put in by the House of Lords.
"We will tomorrow vote to try and reinsert those safeguards that the House of Lords put in to make sure we can have the proper checks and balances."
Responding to Lord Woolf's letter, Prime Minister David Cameron's official spokesman told a daily media briefing in Westminster: "The letter does highlight the very important point that decisions around controlled material proceedings are in the complete control of the judge."
He added: "As regards the vote, this is an important bit of Government policy and the Government intends to see it passed."
Clarke said he had "bent over backwards" to tighten up the legislation and give judges discretion over the cases.
He told BBC Radio 4's World At One programme: "It is less than perfect. If this was a road traffic accident, of course, I would be absolutely outraged.
"The question is, when we are threatened by jihadists in this country, can we possibly give publicly details of the operations we are carrying out, our co-operation with other agencies in America and elsewhere, and so on? Of course we can't."