Bob Geldof has called the Government's plans for holding terror suspects for up to 42 days without charge as "constitutionally repulsive".
The former Boomtown Rats singer hit out as he joined David Davis on the campaign trail ahead of next week's Haltemprice and Howden by-election.
Geldof received a warm reception as he addressed a group of students at Hull's Guildhall.
The rock star, a close ally of Gordon Brown on tackling poverty and repression in Africa, spoke for 30 minutes to local school pupils and constituents.
The Live Aid organiser said as an immigrant from Ireland he owed a great deal of "gratitude" to Britain for allowing him to "get on with it and speak my mind".
"This by-election isn't normal, it is extraordinary," he told the audience.
He said the electorate was not being asked to consider the merits of the Government or opposition but "something profound".
"This time you are being asked to think about who we are. What it is we stand for?"
"This is a fight about illegal boundaries of the state," he added.
"This time, uniquely, we are being asked what kind of people we are and what kind of country we wish to live in. We are being asked to vote about us and we may never get to vote on something so profoundly fundamental."
