The government has set out its blueprint for a second stage of Lords reform to both houses of parliament and triggered a fierce debate across the political divide over the future of the upper house.

Leader of the House of Commons, Robin Cook told MPs that the government's plans would "complement the Commons but will be unable to compete for power with it".

"Reform of the House of Lords should preserve the present balance of power between the two chambers," he said. "The Commons will remain the pre-eminent chamber with the sole right to pass legislation on taxation and the final right to decide on all other legislation."

In the Lords, leader Lord Williams of Mostyn told peers that the white paper provided for "a modern second chamber to play its part in a parliament fit for the 21st century". "We believe that parliament as a whole will be strengthened by these reforms," he said.

Proposals to scrap hereditary peers and to limit the number of elected members of a second chamber to a fifth have provoked anger from opposition politicians - including many on Labour's government benches.

Shadow leader of the Commons, Eric Forth branded the white paper a "fudge" and an affront to democracy.

Dismissing a three month consultation period as an "insult and an absurdity" he called on Labour to withdraw the proposals.

"We will have a continuation and indeed an institutionalisation of Tony's cronies, and the government should either withdraw this white paper or at the very least should refer it to the joint committee of both houses," he said.

In the Lords, Conservative leader Lord Strathclyde branded the plans "shabby and inadequate", in an angry response described by Lord Williams as "uncharacteristically ratty".

With a sideways dig at the reforms' architect Lord Irvine - who chaired the cabinet sub-committee charged with drawing up the plans - he described the white paper as "cooked up in the Cabinet Office over a decanter of port, fit only to get a divided cabinet past the end of the day."

"Whenever I look for a philosophy behind this reform I find just opportunism. Whenever I look for a set of principles, I find only expediency," he said. "The government should be ashamed of this document. It demeans this house, demeans parliament and worst of all it demeans the government itself."

Lib Dem Commons frontbencher, Paul Tyler accused Cook of breaking Labour's 1997 promise to deliver democratic reform: "I'm sure the house will recognise that the rats have got at that since then."

"For the health of parliament we have to go further than this very timid step. Otherwise it's unfinished business, we'll be back again and again and again on this," he said.

And newly elected Liberal Democrat leader in the Lords, Baroness Williams of Crosby demanded a proper parliamentary debate before the Christmas recess.

Arguing that the Lords reform should be part and parcel of wider changes to the Westminster parliament, she complained that the Commons and Lords were both failing to hold the executive to account and said: "We cannot seriously discuss the composition of this house without knowing what are to be our most crucial functions."

Cook told MPs that a mixed membership in Lords - 60 per cent politically appointed, 20 per cent independently appointed and 20 per cent elected - could both reform the second chamber and maintain the constitutional balance to the Commons that lay at the heart of British democracy.

Independent appointments and all future party nominations would, he believed, "ensure a second chamber representative of UK society as it is today, not as it was yesterday".

The white paper the Commons leader said would abolish a government's right to itself set the political balance of peers in the Lords.

"Never again will it be possible for a government to make political appointments predominantly from their own party supporters as the Tories did throughout the 1980s and 1990s," he said.

Praising the reforms for casting out the final remnants of the hereditary peerage from parliament and introducing the second chamber's first-ever elected members to the Lords, Cook highlighted measures ensuring that general election results had an influence on the Lords' composition.

"And they will ensure that it is the British electorate, voting in a general election, who decide the proportions in which party appointments are made and not the government of the day in office," he said

An argument that prompted Forth to demand of Cook, said to be on the side of cabinet ministers who had urged a greater elected component: "Are you content with the 20 per cent elected element in the proposals?"

"We were told at the time the hereditary peers were eliminated that they were an affront to democracy. The question arises whether the government are content that their proposed format for the Upper House is any less of an affront," he said.

Continuing his attack, Forth told Cook that the first round of reforms had been "ill conceived" but that the Tories had been prepared to give the government the benefit of the doubt "because all share an interest in having the most effective possible upper house".

"What we have today falls very far short of that indeed. It satisfies none of the criteria that even the government set out. All in all it is an enormous disappointment," he said. "There is a danger that it is providing a fig-leaf of democracy over what will continue to be a very largely unnecessarily unrepresentative and appointed body".

Hitting back at the Conservative record on Lords reform Cook claimed that Tory concerns over democracy in the upper house were "a new departure".

"In 18 years they never once proposed a single elected member of the House of Lords and never made a single proposal for reform," he said.

But in an indication of the parliamentary hurdles ahead for the reforms, the ground that needs to be covered on the government's own benches and perhaps a sign that concessions may emerge in the consultation period , Labour MPs have lined up to criticise the plans.

David Clelland, MP for Tyne Bridge, described the white paper as representing the "worst of all worlds" with a set up that was "part-patronage, part-appointment part-elections [causing] a clash of mandates".

Pendle MP Gordon Prentice said that the government had failed to put forward proposals that would create a modern second chamber and asked: "Surely legitimacy only comes from elections?"

Cook answered those critics calling for an elected House of Lords claiming it would be a recipe "conflict and competition".

"Personally I do not want to carry through a measure which will result in undermining the powers and prerogative of this chamber," he told his backbenchers.