LONDON (AFP) - The Duchess of Cambridge's uncle has been fined £5,000 (S$9,000) for punching his wife in the face during an argument, with the magistrate who sentenced him on Tuesday (Nov 28) calling him a "nasty drunk".

Gary Goldsmith, 52, admitted to using a closed fist to hit Julie-Ann Goldsmith, who fell to the ground and was left semi-conscious outside their central London home in the early hours of Oct 13.

Goldsmith, who is the younger brother of Carole Middleton, mother-in-law of Prince William, was spared prison but was also given a 12-month community order that will include 20 rehabilitation sessions.

The court heard the couple began to argue while in a taxi after a charity event, then continued the argument on the street outside their home.

Chief Magistrate Emma Arbuthnot said Goldsmith had called his wife "a nothing and whore" during the argument, saying he was a "nasty drunk".

After falling to the floor, his wife remained flat-out with her eyes closed for around 15 seconds before waking up and staggering to her feet, the prosecutor said.

In a victim impact statement, she said she had been left feeling "extremely anxious and very stressed and suffering panic attacks".