South Yorkshire peer Lord Ahmed of Rotherham is backing calls for a second referendum on leaving the European Union.
The former Labour peer and now independent voted to leave the EU but today said he will back the Liberal Democrats in their push for a second referendum.
He claimed a significant number of people who backed the Leave campaign have since changed their minds and would rather remain in the EU.
Lord Ahmed said: "I honestly don't think we have had a real debate in relation to how it will affect individually our jobs and our prosperity, and people have now realised.
"I know lots of people who have said I voted for leave but I think that was a mistake."
Peers in the House of Lords will today debate the European Union (Notification of Withdrawal) Bill, which once passed will formally pave the way for Britain to leave the EU.