One heckler threw a shoe at Zardari during the event, missing the president, while outside the convention center police cordoned off more than 100 protesters.
Zardari told supporters his trip to Britain had been a success, and that he had raised tens of thousands of pounds for flood victims at home. Thousands crowded into the convention center in the English city of Birmingham to listen to the visiting leader and other speakers from his Pakistan People's Party.
Some protesters placards that read "USA. out of Pakistan and Afghanistan." Many Pakistanis are angry about US-led forces within Pakistan and increasing military operations in the frontier and tribal border areas. Others held banners complaining that Zardari chose to continue on his foreign trip at a time of national disaster.
"Too many Pakistani civilians have lost their lives because of this foreign-led war," said a protester who identified himself as Iqbal Najid, 32.
Earlier in the day Zardari's son and co-chairman of the PPP, Bilawal Bhutto Zardari, appealed for donations to help Pakistani flood victims in London.
Many had expected Zardari's son to join him at the rally and use the occasion to launch his political career, but the 21-year-old angrily rejected such speculation. Instead, he only appeared before the media briefly at Pakistan's High Commission in London, where he accepted donations for flood victims and defended his father's trip abroad during the disaster.
"My father's doing all that he can to aid the people of Pakistan. His personal presence in Pakistan could not have done there what he did here," Bhutto Zardari told reporters.
Pakistani officials estimate that as many as 13 million people have been affected in the floods and some 1,500 have died. More rain is expected in the coming days as the bloated Kabul River surged into Pakistan's northwest.
"This is not a time to play politics. We need to do what is necessary to help our brothers and sisters in Pakistan," Bhutto Zardari added.
Although his father said it was only a matter of time before his son carried on the family's political dynasty, Bhutto Zardari became irritated at reporters' suggestions that he was using his father's visit for his political gain and said he never intended to join the rally.
He would not launch his political career "until I complete my education, as I promised my mother," he said.
Former Prime Minister Benazir Bhutto was assassinated at a political rally in late 2007. Her father, the founder of PPP, was hanged in 1979.
Bhutto Zardari said he would focus on raising money for flood victims in Britain and had no plans to travel to Pakistan soon. Still, many party supporters at the rally Satruday were more interested in talking about the young Oxford graduate than about his father.
"We want Bilawal to pick up where his mother left off," said Samina Mohammed, 25. "He can give us the best hope for this country." Plagued by allegations of corruption and money laundering, Zardari hasn't enjoyed the same support as his slain wife or other members of the Bhutto clan.
The leader faced domestic criticism for going overseas while his nation battles deadly floods, and his trip had also been fraught because it came so soon after British Prime Minister David Cameron accused Pakistan of exporting terror. The remarks caused a diplomatic row, in part because they were made during Cameron's visit to India, Pakistan's nuclear rival.
The Pakistani president rejected the criticism, saying that it was terrorists who killed his wife and who were terrorizing his country. Some 2,500 Pakistani security officials have been killed in battles with militants over the years, and many more civilians have been killed in attacks. On Saturday, the militant Taleban claimed responsibility for the killing of eight foreign aid workers in neighboring Afghanistan.
In an interview with The Associated Press on Friday, Zardari also defended his trip, saying Prime Minister Yousaf Raza Gillani had been dealing with the floods. Prior to his British visit, Zardari was in France where he visited a family chateau and met with French President Nicolas Sarkozy. He will travel to Syria from Britain.
Analysts predict Zardari's PPP will suffer during the next national elections in 2013 because of Zardari's low approval ratings and the severe challenges currently facing the country.
Nearly 10,000 members of the party live in Europe, most of them in Britain.
Pakistan is one of Britain's most important allies in fighting terrorism. Nearly 1 million people of Pakistani origin live in Britain, and Pakistani intelligence has been crucial in several terror investigations, including the 2005 suicide attacks that killed 52 London commuters and a 2006 trans-Atlantic airliner plot. The ringleader of the 2005 suicide bombings in London and several others reportedly received terror training in Pakistan.
Zardari has headed a coalition government since unseating Pakistan's Gen. Pervez Musharraf. The ex-military leader was in power-sharing talks with Bhutto shortly before her assassination at a political rally in December 2007.
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