Peers attack Nick Clegg's Lords reform plans
Government plans to replace the House of Lords with a largely elected second chamber have come under sustained attack from peers of all parties.
Lib Dem peer Lord Rodgers said the plan, spearheaded by his party leader Nick Clegg, would "run into the sand".
And ex-Cabinet Secretary Lord Armstrong said he foresaw "much blood in the Thames" as a result of clashes between the Commons and any new assembly.
Ministers say an elected chamber would have proper legitimacy.
Peers have been discussing proposals to dramatically reduce the size of the Lords to just over 300 people and elect 80% of its members, starting in 2015.
On the second day of a two-day debate about the future of the Upper House, Lib Dem peers were among those to criticise the deputy prime minister's blueprint.
Lord Rodgers said he had opposed an elected second chamber for 20 years despite his party's longstanding support for it and he had not changed his mind.
"I fear this Bill, as it stands, will run into the sand," he said. "With the coalition's heavy legislative programme for this Parliament, Lords reform will inescapably block or delay more important issues.
"There will be no consensus, which there ought to be in a very major change in the nation's constitution."
Fellow Lib Dem Lord Glasgow, one of 92 remaining hereditary peers in the Lords, said his party's proposals "made no sense at all".
"I have always believed, and I thought this was a fairly general view, that the House of Lords justified its existence by being a very effective revising chamber.
"Its primary purpose was to scrutinise and improve government legislation, not, like the House of Commons, to be a party political slanging shop. It succeeds in being an effective revising chamber largely due to the quality and variety of its inmates."
And Lord Armstrong, the former head of the civil service, predicted frequent disagreements between the Commons and the new assembly in the event of its members being able to claim a democratic mandate.
"I foresee serious breakdowns in the relationship between the Commons and the Lords and the River Thames running under Westminster Bridge with much blood," he told MPs.
All three of the UK's largest parties committed themselves to changing the make-up of the Lords in their 2010 general election manifestos but there has been little sign of agreement on the way forward.
Mr Clegg has asked a committee of peers and MPs, to be led by Labour MP Lord Richard, to examine the proposals - which would see a largely elected "senate" with members serving 15-year terms.
Lord Strathclyde, the leader of the House of Lords, has made clear the government is committed to seeing the first elections to the new body taking place in 2015.
'House in order'
And in an impassioned defence of the plans on Monday, former Lib Dem leader Lord Ashdown said constitutional reform was needed to "bridge the dangerous gap between the government and the governed".
"This is not about what the public wants," he said. "It is about us putting our house in order."
The current House of Lords lacked legitimacy, he argued.
"We have to be part of a reform that reconnects politics with the people of this country. And if we are not, I believe our democratic institutions will fall into atrophy and may suffer further in the decline in confidence of the people in this country
Labour have said they will oppose the proposals as they stand while many Tory MPs also object to them.