The actor celebrated his 41st birthday while staying at the exclusive Claridges hotel, according to The Times of India.
A source told the paper: "Last week they were shooting for Agent Vinod, but nobody knew what Kareena had planned for Saif's birthday. She requested Saif's production partner Dinesh Vijan for five days off from the shoot to whisk him off to London.
"This year, Saif's birthday plans have been kept completely quiet and nobody except their families know where they are. They are staying at their favourite hotel Claridges.
"Kareena even made all the arrangements for the birthday dinner on Tuesday night at an exclusive resto-bar in London."
The actress kept the plans lowkey because her boyfriend prefers to keep their personal lives private, the source said.
In June, it was rumoured that Kapoor would have her waxwork at Madame Tussauds unveiled on her boyfriend's birthday.
The pair are reportedly planning to get married by the end of 2012 and set an official engagement date around Valentine's Day.
