The disclosure raises questions about the closeness between the Prime Minister and Mrs Brooks, the former tabloid editor who quit as chief executive of News International at the height of the phone hacking scandal last summer.
It emerged this week that Mrs Brooks was lent a retired police horse by the Metropolitan Police for two years. The horse, called Raisa, was stabled at her farm in the Cotswolds from 2008 to 2010, before it was handed back to Scotland Yard. It was put out to pasture in Norfolk and has since died.
An aide close to the Prime Minister confirmed for the first time that Mr Cameron had gone riding with Mrs Brooks’ husband Charlie, a racehorse trainer and an old friend from his Eton schooldays.
The source said that it was “possible” that one of the horses could have been Raisa, because Mr Brooks had lent a number of horses to Mr Cameron over the years. The aide said: “It is possible. He used a number of Charlie’s horses.”
Mr Cameron had no recollection of ever going riding with Mrs Brooks, however. The aide added: “He never rode with Rebekah Brooks. He has no recollection of ever going riding with Rebekah Brooks.”