Speaking in Glasgow, the Prime Minister said: "I am sorry about what happened. I have said all along when I saw this first I was horrified, I was shocked and I was very angry indeed."
He said he wanted to reassure people everything was being done to clean up politics in Britain and stressed he had written to all those affected to express his regret.
"We have ensured there are new rules to ensure this cannot happen again," he said.
Asked if the buck stopped with him, he said: "I take full responsibility for what happens, that is why the person responsible went immediately." It's been a long time coming, and - to my ears - it still sounds a little too equivocal to draw a line under things. A good indication of whether there's any meaning behind it will be whether Brown maintains his coterie of bruisers and attack dogs. For now, I remain sceptical.