The veteran hair guru passed away at his home in Los Angeles home in May (12) at the age of 84 following a battle with leukaemia.
A memorial was held at St Paul's Cathedral in the U.K. capital and Sassoon's famous friends and clients flocked to pay tribute to him at the ceremony.
Caine, who was joined by his wife Shakira, Irons, fashion designer Zandra Rhodes and British Vogue editor Alexandra Shulman all turned out to pay their respects.
Caine told reporters, "(It's) a sad day but we get a chance here to celebrate his life."
Sassoon helped revolutionise women's hair in the 1960s by coming up with the 'bob' cut and snipping Mia Farrow's hair into a pixie crop for her film Rosemary's Baby.