The tape, which aired on Arabic news station Al-Jazeera, was the first video to directly focus on Britain's foreign policies.
Al-Zawahiri did not directly claim al-Qaida carried out the July 7 or July 21 attacks, but did place the blame with British Prime Minister Tony Blair and his decision to deploy troops in Iraq.
"Blair has brought to you destruction in central London, and he will bring more of that, God willing," al-Zawahiri said in the Al-Jazeera excerpts.
Blair's office is declining to comment to the media on al-Zawahiri's threats.
Blair has in the past strongly rejected any tie between the attacks and Britain's role in Iraq. British police haven't established any firm links between the bombings and al-Qaida, but two groups linking themselves to al-Qaida claim responsibility for the attacks.
Al-Zawahiri also repeated previous threats against the United States, saying tens of thousands more American forces will die unless its military leaves Iraq.
"What you have seen in New York, Washington and Afghanistan, are only the initial losses," he said in the broadcast, referring to the Sept. 11 attacks on the United States for which al-Qaida claimed responsibility.
"Our message to you is clear, strong and final: There will be no salvation until you withdraw from our land, stop stealing our oil and resources and end support for infidel, corrupt (Arab) rulers," al-Zawahiri said.
He also suggested Western nations that have provided the United States with troops would also be attacked if they continued to ignore a truce offered by bin Laden in April 2004.
"Hasn't Sheik Osama bin Laden told you that you will not dream of security before there is security in Palestine and before all the infidel armies withdraw from the land of Muhammad?" al-Zawahiri said.
President Bush said Thursday that the threats will not drive the United States out of Iraq or the broader Middle East.
"We will stay on the offense against these people," President Bush said. "They're terrorists and they're killers and they will kill innocent people ... so they can impose their dark vision on the world."
No other countries were directly named, but al-Zawahiri appeared to be referring to the 2004 terror attacks in Madrid, Spain that were linked to al-Qaida. The train bombings killed 191 people.
Al-Zawahiri was last seen in a video aired by Al-Jazeera in June when he called for an armed struggle to expel "crusader forces and Jews" from Muslim states and said peaceful change was impossible.