The protesters marched under heavy police presence and carried placards reading: "Tories Out" and "Cameron Must Go".
Protest organiser Abi Wilkinson tweeted: "The tropical tax haven party is heating up nicely, and the sun is coming out!"
Cameron had admitted earlier this week that he benefited from a Panama-based offshore trust set up by his late father but sold his stake months before he became Britain's prime minister in 2010.
The admission came five days after the leak of millions of secret documents from a Panama-based law firm which revealed that the prime minister's father, Ian Cameron, who passed away in 2010, ran an offshore firm under the name Blairmore Holdings.
Addressing party members at the party's spring conference in London today, he said that he had learnt lessons over the past week.
"It has not been a great week. I know that I should have handled this better, I could have handled this better. I know there are lessons to learn and I will learn them," he said at the start of his address to Tory activists.