"Katrina and Ranbir took a British Airways flight to London at 1.50am on Thursday. They will be there for a week. It was an impromptu decision to fly out of the country; she was so tied up with different shoots that she thought she would have a working birthday. But before leaving, she had a quiet dinner with five or six close friends since she is not a big believer in the idea of elaborate birthday parties," says a source close to the actress.
While Kat's sisters are in London, her mother is said to be in south India where she supports a charitable organisation.
"They might meet her sisters there, but the actual reason behind this getaway is to spend quality time with each other. In any case, she visits her family once a year on Christmas," adds the source.