The Michelin-starred presenter of the TV series Kitchen Nightmares wrote the emotional appeal after falling out with Chris Hutcheson – the father of his wife, Tana, 37, and his mentor and business partner for 12 years – who was dismissed last month as chief executive of Gordon Ramsay Holdings (GRH).
In the letter, addressed to Greta Hutcheson and written on his 44th birthday, Ramsay says: "This has to be one of the most painful letters I've ever had to write. Listening to Tana in floods of tears reading your letter asking that she stays away from her family is so awfully wrong."
He adds: "Removing my father-in-law from my business has been the hardest and most important decision in my entire life," but goes on to accuse Hutcheson of being manipulative and controlling.
The letter, published in the London Evening Standard newspaper, follows an interview given by Hutcheson, 62, to a Sunday newspaper in which he alleged he was sacked in a "public hanging" and claimed Ramsay had become a "monster" who had poisoned his daughter against him and become "warped" by the celebrity lifestyle.
The sacking, on 16 October, ended what was widely regarded as one of the strongest partnerships in the restaurant industry. Hutcheson said in the interview that his daughter, who has reportedly been staying in Los Angeles with Victoria and David Beckham since the row, had not spoken to him since and had refused to return her mother's emails, texts and calls.
Sources said Ramsay's decision to write the open letter came during an "incredibly emotionally fraught" time.
It will be interpreted as a response to Hutcheson's very public claims.
In the letter, Ramsay begs his mother-in-law not to punish his wife and children. "I know how hard this must be for you, Greta, and I'm not expecting a birthday card today, but your punishment of your daughter and our four children, for all the wrong reasons, it's so sad. She's an amazing woman and you've been a fantastic mum, please don't stop."
Were down to involvement with drugs
He adds Hutcheson recently "suggested my mood swings were down to involvement with drugs; my God did that hurt. How dare he ever suggest this on the back of my frustration and dealings with my younger brother and his addiction?"
He reveals he hired a private detective to look at Hutcheson's "complex life" and that his away days were "rarely what I thought they were". "But beyond that one of my biggest concerns was the business; signing huge contracts in my name and furthermore discovering emails were being looked at," he wrote.
He said Hutcheson had run the business as a "dictator" and there were looks of "relief and joy" of the faces of staff when he announced Hutcheson's departure. The relationship began in 1998 when the two set up Gordon Ramsay Holdings two years after Ramsay married Tana. Their empire included restaurants in Europe, Asia, the Middle East, Australia and the US.
Ramsay's first restaurant, Aubergine, opened in 1993 and gained a Michelin star within 14 months. He left in 1998. With Hutcheson's help he set up Gordon Ramsay at Royal Hospital Road, which still holds three Michelin stars. It catapulted Ramsay to TV fame, and allowed him to open a series of restaurants in London.
Over-rapid international expansion, particularly in the US, in 2008 lost £8.3m and bought Ramsay close to administration. Gordon Ramsay Holdings International (GRHI) closed restaurants in New York, Los Angeles and France, which are now run on a consultancy basis. However his restaurant empire in the UK reportedly doubled profits to £4.2m in the 11 months to the end of August, up from £2.47m for the same period a year ago. The split came a week after Angela Hartnett, one of the most prominent chefs in the Ramsay empire, bought out his share in her Michelin-starred restaurant Murano, in Mayfair.
There was no comment from the Hutchesons, although a friend denied he had accused Ramsay of taking drugs, telling the Standard: "It would have been nice to have ended a 12-year relationship in an orderly way over a drink, but Gordon chose to lock him out of the office without notice. That's what's caused the family rift."