• Tony Blair has his blood pressure taken by Nurse Paula Martin at Alexandra Avenue Health and Social Care Centre. (PA)
Visiting Harrow in north-west London, Mr Blair insisted Labour still had "every chance of succeeding" in the General Election.
Questioned about whether Mr Brown had failed in his time at Number 10, he said: "No I don't think he's failed at all."
Asked about the prospect that the party could come third in the share of the vote on May 6, the former PM replied: "I don't believe that will happen. I believe Labour has every chance of succeeding."
He said the TV debates had focused the campaign on the "ups and downs", but he added: "When you get into the final days people will really focus their minds on who's got the best ideas for the future."
As he had his blood pressure taken at a polyclinic in the Labour-held constituency, Mr Blair joked: "The question will be, is it better or worse than it used to be?"
An onlooker interjected: "Or is it better or worse than Gordon's?"
Mr Blair responded: "It's a tough job being Prime Minister – I know."
Mr Blair described Mr Brown as "completely honest" and said he had the "energy and drive" to take Britain forward.
Speaking at Alexandra Avenue Health and Social Care Centre, he said: "I think if people actually look and listen to the substance they will see somebody who is completely honest, who knows his facts, knows exactly the policies that the country should follow."
He said the TV debates were dominated by "who's up and who's down and all the rest of it".
"But when you come to a clinic like this... and the real question for the future, for the country, is this going to be the way that we are going to go or not? And that's the key issue," he added.
Dr David Lloyd, who runs the health centre, showed Mr Blair around along with International Development minister Gareth Thomas, who is the Labour candidate in Harrow West.
The former PM had his blood pressure taken by nurse Paula Martin, who was the onlooker who suggested it might be lower than Mr Brown's.
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• A car crashed into a bus shelter today as Gordon Brown was launching a new Labour Party poster nearby.
The Volkswagen Golf smashed into the shelter on a traffic island in Hockley, Birmingham, yards from the car park where the launch was taking place.
The Prime Minister carried on with his speech at the event, aimed at re-energising his campaign in the final week of the election, as emergency services went to the scene.
Witnesses said people in a passing refuse truck were jeering at the launch as it drove around the traffic island just moments before the crash.
The car driver was uninjured, police said.