The open letter comes ahead of a government green paper tomorrow that is expected to call for a narrower range of BBC programming.
In the letter, the celebrities wrote, "In our view, a diminished BBC would simply mean a diminished Britain."
Stephen Fry, screenwriter Richard Curtis and Rachel Weisz are also the signatories on the letter which emphasises the "concern that nothing should be done to diminish the BBC or turn it into a narrowly focused market-failure broadcaster".
"Britain's creative economy is growing and enjoying unprecedented success. The BBC is at the heart of this as the global showcase for our creative industries. The BBC is trusted and loved at home by British audiences and is the envy of the world abroad," the letter reads.
Culture secretary John Whittingdale is expected to set out a range of proposed reforms in his green paper tomorrow, among them the scrapping of popular shows like "The Voice" and the replacement of the licence fee with a household tax.
