Tony Blair says it is "ridiculous" to suggest that he should not back England in the World Cup just because he is the prime minister of four home nations.
Mr Blair was asked if he would be following Ms Jowell's example
He also refused to say whether he will be following Culture Secretary Tessa Jowell's example and flying the flag of St George on his official car.
The PM spoke out after he was pressed to say how he would be supporting the team during a webcast interview.
He said he was sure Gordon Brown, a Scot, would also be backing England.
The questions arose after two St George's flags were seen flying proudly from Ms Jowell's official vehicle.
Environment Secretary David Miliband has said he will also be flying an England flag from his ministerial car.
Asked if he would be doing the same, Mr Blair replied: "I'll certainly be supporting the England team very strongly.
"I will have to reflect on the best and most appropriate way to do that."
But when it was suggested that some people did not think the prime minister of four nations should be backing just one of them, he replied: "I think that's rubbish.
"The idea that it's wrong to put the England flag up - come on. Why not? It's the flag of England. It would be completely absurd.
"It's just ridiculous. Why can't people support the England flag? Of course they can. I don't understand that one at all."
Asked if the chancellor, his Scottish neighbour, would be backing England, he said: "He's perfectly happy to support the England flag in terms of when they are in the World Cup."
When Ms Jowell, who department is responsible for sport, was asked who she thought was going to win the cup, she gleefully pointed towards her ministerial vehicle, which is now bedecked in flags, to declare: "There's only one England".