Mr Clarke revealed that more than one-third of all backbench MPs and most Tory frontbenchers had backed proposals to replace the House of Lords with a senate-style body.
The campaign was launched as 131 MPs signed an early day motion demanding that "the composition of the second chamber of Parliament should be determined by election".
Accompanied by Charles Kennedy, the Liberal Democrat agriculture spokesman, and Mark Fisher, Labour's former arts minister, Mr Clarke said the motion would send a clear message to the Royal Commission on Lords reform.
"There is strong and growing cross-party support in the House of Commons for an elected second chamber... In the 21st century, only the ballot box can provide the second chamber with sufficient legitimacy for it to perform a constitutional role."Reuse content