Justice Secretary Chris Grayling has set out the terms for the pre-legislative inquiry into whether prisoners should be granted to right to vote.
He said: "Parliament is sovereign in this area.
"Nobody can impose a solution on parliament but the accepted practice is that the United Kingdom observes its international obligations."
Shadow justice secretary Sadiq Khan said allowing prisoners serving less than four years to vote would lead to 30,000 inmates going to the polling stations.
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