Britain's Duchess of Cambridge celebrated her 30th birthday with a quiet dinner' yesterday, it has been reported.

Following the royal couple's glamorous red carpet appearance at the War Horse premiere on Sunday, last night Duchess Catherine dressed down to attend an intimate birthday dinner with family and close friends.

According to British newspaper The Mirror the celebration was planned by the couple's best friends, including nightclub owner Guy Pelly, and is said to have taken place in a private dining room near Kensington Palace.

A source explained that following her huge wedding in April and a successful first year as a member of the royal family, Catherine preferred a pared down celebration.

"Yes, it's a milestone birthday, but it's been a year of milestones for Kate and she's happy to keep things low key," a source commented ahead of the event. "She will be celebrating it but it will just be with a few people and it won't be anything fancy. Of course she wants to raise a glass to an incredible year and to this new decade of her life but she doesn't feel the need to go wild."

The Duchess' siblings Pippa and James Middleton are believed to have attended the birthday dinner, but Catherine's brother-in-law, Prince Harry, was needed on base at RAF Wattisham in Suffolk.

Following last night's intimate celebrations, the Duke and Duchess of Cambridge are believed to have returned to their marital home in Anglesey, Wales.