Some held up shoes to pictures of Zardari, while others held placards reading "1,000s dying, president is holidaying".
One of the demonstrators told Al Jazeera: "He's here living in five-star hotels while whole villages have been wiped out. I just think it's a shame."
Another said: "He should be over there looking after the people but obviously he doesn't see them as people. He sees them as nobody, otherwise he would not be here."
Zardari was already unpopular before the floods hit Pakistan and he has been nicknamed "Mr 10 per cent" over widespread allegations of fraud.
"Zardari's poll ratings are the lowest they've ever been," our correspondent said.
"There are elections in Pakistan next year. It's thought that the PPP will do exceptionally bad and most of that will be because of Zardari."
The rally in Birmingham had raised expectations that Bilawal Bhutto Zardari, son of the president and the assassinated prime minister Benazir Bhutto, would make his maiden political speech after graduating in June from Oxford University.
But in an apparent attempt to appease anger over the handling of the floods which have killed at least 1,600 people, the 21-year-old cancelled plans to attend and said he would instead stay in London to collect donations for flood victims.
Bilawal defended his father's visit to Europe, saying the president was raising much-needed funds.
"He's doing the best he can and what he thinks is best to help the people of Pakistan," Bilawal said.
"His personal presence in Pakistan would not be able to raise this much money."
He said multi-million dollar donations had been made by France, Britain and Abu Dhabi.
The PPP is co-chaired by Zardari and his son.
Asked whether he was using his father's UK visit to launch his own political career, Bilawal: "That's all lies."
During his trip, President Zardari met David Cameron, the British prime minister, amid a diplomatic spat between the two countries over Cameron's remarks that Islamabad was "exporting terror" and looking "both ways" in the battle against the Taliban.
Zardari hit back at the allegations, arguing that Pakistanis are often victims of attacks on their own soil and insisting that his government is committed to fighting armed groups in the region.
In Friday's meeting, the two leaders agreed to put the dispute behind them, with Zardari insisting that the two countries will "stand together" in the face of difficulties.