Lord Falconer of Thoroton, in charge of reform of the voting system, said calls for reform are backed by many Labour MPs, including ministers.
"The detail of the debate is interesting, there are arguments that can be made both ways, but it's a major piece of constitutional reform which would take very significant amount of legislative time and political capital," he said.
His comments follow The Independent's Campaign for Democracy, in which almost 40,000 people have demanded a review of the voting system.
There is "no consensus in the country" for a change, he said, but added: "That is not to say there aren't members of the Government, of the Parliamentary Labour Party, of other parties who think it is a worthwhile thing. That may be right, but it is not something we think should be a priority at the moment."Reuse content