The government's proposed changes to the electoral registration system have been described as "potentially toxic" for British democracy by a Labour former justice minister.
Lord Wills tabled a debate on government policy on electoral registration on 12 January 2012, in which he claimed millions of people could be denied their democratic right to vote as a result of the changes.
The government is planning a switch from household to individual voter registration aimed at reducing fraud.
The Electoral Commission says a change is needed but urged ministers to hold a household canvass in 2014 to keep numbers up.
Lord Wills said he supported individual registration but warned of a "severe risk" of "significant" falls in the number of British voters able to vote.
Plans to remove the civic and legal duty to register to vote and abolish the annual household canvas in 2014 risked making the register "even less complete", he added.
"This is potentially toxic for our democracy. The party that will suffer least, if at all, from the fall in registration is the Conservative party," Lord Wills said.
His argument was supported by another Labour peer and former chairman of the Local Government Association, Lord Beecham, who said it would be a "mistake" to make registration voluntary.
Similarly, Liberal Democrat Lord Rennard, a former director of campaigns and elections for the party, argued that removing the legal requirement to register would "take a great risk to the quality of our democracy for no benefit whatsoever".
Conservative peer Lord Lexden pointed out it was a criminal offence in Northern Ireland not to complete a voter registration form, but that no such provision was currently being proposed for Britain.
"Equity demands uniformity," he said.
Another Conservative peer, Viscount Astor, called for more steps to ensure servicemen and women working abroad were able to vote.
Shadow justice minister Lord Bach urged the government to address the "scandal" of the "huge" number of unregistered British voters - which rose to six million in December.
Winding up the debate for the government, Lord Wallace of Saltaire said the UK was one of the few countries left to have a household basis registration and that the case to moving to individual registration was in every party manifesto and "generally accepted".