It is true that there is corruption in Afghanistan, much of which is down to the regime installed by the USA and Great Britain. Nigeria also has a chronic problem with corruption which is actively fed by the money laundering expertise of British banks. The corruption in these countries has been responsible for underdevelopment and systemic inefficiency.
However, Great Britain historically and under David Cameron has not been a corruption free state. There has been the cash for questions, cash for peerages, MPs expenses, British Aerospace bribery, Libor rate rigging, mortgage payment protection, HSBC money laundering, Weat Yorkshire police, BHS pensions scandals; to name but a few. So it would appear that there is an equally fantastic amount of corruption going on in Britain itself.
Addressing corruption in the developing world is necessary but mocking and deriding the countries does call into question how sincere Great Britain's efforts really are. It will be difficult to win the trust of people who are held in such low regard. David Cameron may point the finger at others for being corrupt but the fingers pointing right back at him suggest he has a lot of work to do to clean up corruption back at home.