British Prime Minister David Cameron has called Nigeria and Afghanistan "possibly the two most corrupt countries in the world". 

Cameron was caught on camera making the remarks to the queen and Archbishop of Canterbury Justin Welby at an event in Buckingham Palace, ahead of an anti-corruption summit he is hosting on Thursday. 

Both Nigerian and Afghan presidents are due to attend the summit in London. A spokesman for the Nigerian president called Cameron's comments "embarrassing", and stressed things are changing in Nigeria.