Putin, via his spokesman, said: "Britain is just a small island, no one pays any attention to them, except oligarchs who bought Chelsea football club."
Cameron replied: "Britain may be a small island, but I would challenge anyone to find a country with a prouder history, a bigger heart or greater resilience.
"Britain is an island that has helped to clear the European continent of fascism - and was resolute in doing that throughout World War Two.
"Britain is an island that helped to abolish slavery, that has invented most of the things worth inventing, including every sport currently played around the world, that still today is responsible for art, literature and music that delights the entire world.
"We are very proud of everything we do as a small island - a small island that has the sixth-largest economy, the fourth best-funded military, some of the most effective diplomats, the proudest history, one of the best records for art and literature and contribution to philosophy and world civilisation.
"For the people who live in Northern Ireland, I should say we are not just an island, we are a collection of islands. I don't want anyone in Shetland or Orkney to feel left out by this.
"I'm thinking of setting this to music..."
The strangest thing is that Cameron chose Google+ as his medium of choice for this missive: https://plus.google.com/+DavidCameron/posts/ZAhgNM2in2Q