Tony Blair was responding to an opposition Conservative politician who asked him if he intended to involve himself personally in the matter.
"This is a huge issue of sensitivity for the Egyptian authorities as well as our own," Blair said in the House of Commons on Wednesday.
"I have instructed our ambassador in Cairo to call on the Egyptian foreign minister to raise our concerns about the case."
He added: "I can assure you that we will keep track of this case very, very closely indeed, but I do ask you to understand also that, because of the history of these issues within Egypt itself, it is a sensitive matter for the Egyptian authorities too."
The three British nationals - Majid Nawaz, 28, Reza Pankhurst, 27, and Ian Malcolm Nisbett, 24 - and 22 Egyptians have been held since April 2002.
"This is a huge issue of sensitivity for the Egyptian authorities as well as our own. I have instructed our ambassador in Cairo to call on the Egyptian foreign minister to raise our concerns about the case"
British prime minister
They were detained on charges of having tried to revive the Islamic Liberation Party, also known as Hizb al-Tahrir.
Verdicts in the trial were recently postponed until March - the latest in a series of delays in the case.
Blair said he was aware that Foreign Office Minister Baroness Symons had met the families of the men involved last week to hear their concerns.
At the first court hearing in Cairo last October, Pankhurst told reporters he and other defendants had been subjected to prolonged torture which prompted them to make confessions they later retracted. All the defendants pleaded not guilty.
The three British accused said they were in Cairo to study Arabic.
The Islamic Liberation Party seeks to restore one Islamic government for all Muslim states. It has no history of political violence.
It has had a presence in several Arab countries, including Egypt, where it was disbanded after an attempted coup in the 1970s.