In an interview with Aljazeera.net, Paul Bigley, 54, said he would not be quiet over the "frustrating" situation he and his family are in, despite the British Foreign Office issuing "strict instructions" for them to resist commenting on the capture.
Bigley's brother, Kenneth, 67, was seized along with two Americans in Baghdad on Friday and faces execution by a purported Iraqi group if their demands are not met.
Another American hostage, Eugene Armstrong, who was captured along with them, has been beheaded, according to footage shown on an internet site overnight.
Although the British government has said it is "doing everything" it can to save his brother's life, Bigley says "Tony Blair is going through the diplomatic instruction book" and not doing enough.
"They [Blair and his government] are ignorant. They have no ears for the situation on the ground.
"The whole attack on Iraq was absolutely ridiculous, unfounded and stupid. And I will not be told to shut up, not about an important situation like this," he said.
Tony Blair (L) and Iyad Allawi are
accused of not doing enough
"I understand the Middle East, I truly do," Bigley continued. "I understand the Palestinian question which the whole world is ignoring and which is the core of the whole problem that is going on in the world today."
As a businessman, who has worked in the Middle East for 30 years, Bigley said he "feels the frustration of all Arab nations ... the fact that nobody is listening to the Palestinians' problems".
"People are becoming frustrated. People are killing themselves... How far can a human being go but to sacrifice his or her life for the cause they believe in?
"History always speaks the truth," he said. "And history will speak the truth about the sham, the so-called war that is taking place and killing so many lives."
Speaking about interim Iraqi Prime Minister Iyad Allawi, who is in London for talks with Blair, Bigley said: "All Mr Allawi needs to do, if he has any feelings, is to pick up the telephone and offer an olive branch."
"History always speaks the truth... And history will speak the truth about the sham, the so-called war that is ... killing so many lives"
Allawi, he said, should respond to the captors' demands and "order the release of maybe five or 10 female prisoners immediately".
These women, he added, "are not political prisoners. They are domestic prisoners. They should not be there".
"The Americans, they are trigger happy. They are going completely crazy."
Choking back tears, Bigley begged for "mercy" to be shown towards his brother and his brother's colleague.
"The Middle Eastern people is a beautiful people. It is the outside that is causing all the problems," he said.