Prime Minister thanks Sir George for his "support and friendship"

Mr Cameron sent a letter to Sir George on July 15, after the former Chief Whip announced he would step down from this position ahead of his retirement at next year’s General Election.

As reported on The Gazette website, 72-year-old Sir George made the announcement on Monday, ahead of Mr Cameron’s cabinet reshuffle.

In his letter to Sir George, Mr Cameron said: “We have been here before – your safe passage to the relative calm of the backbenches in 2012 in the end never materialised. Indeed, when I wrote to you in September 2012 to thank you for your past outstanding contribution to our Government, neither of us thought I would be writing a further letter two years later!”

He added that Sir George took on the role of Chief Whip at “a very sensitive time” and said he had given “exemplary service in this role, as I knew you would.”

He added: “I remain incredibly grateful to you for agreeing to return to Government and for the further contribution you have made. At what has sometimes been a challenging time for the Parliamentary Party as we entered the final years of this Parliament in coalition, you have brought your unrivalled Parliamentary and Government experience to bear.”

He described Sir George as “the most loyal and dependable of colleagues, a calm and knowledgeable presence at the heart of our Government”, adding: “Forty years since you first entered Parliament and 38 years since your first Front Bench role, you have every right to look forward to your retirement from the House next year. Over the decades you have brought so much to Parliament, to our Party, to Government, and to our country.

“Both politics, and, more widely, public service will lose a widely respected champion when you stand down in 2015 after a remarkable career in Parliament. I am deeply grateful for all that you have done both for this Government and for our Party.”

Mr Cameron ended his letter by thanking Sir George for his “support and friendship”.