Queen Elizabeth II was caught on camera describing members of a Chinese delegation on a state visit last year as ‘very rude’, in a rare diplomatic gaffe by the British monarch.

Her comments, aired on Wednesday, came just hours after Prime Minister David Cameron also made inadvertent public remarks, referring to the ‘fantastically corrupt’ countries attending a summit in London.

Dressed in a pink coat and hat with white gloves, the queen was caught on camera during a garden party at Buckingham Palace on Tuesday making unguarded comments about a Chinese state visit last year.

Police commander Lucy D'Orsi was introduced to the queen as the woman who oversaw security for the visit of President Xi Jinping and his wife in October, to which the monarch replied: ‘Oh, bad luck’.

D'Orsi was recorded as saying, ‘I'm not sure whether you knew, but it was quite a testing time for me,’ to which the queen is heard replying: ‘I did’.

The queen went on to say to D'Orsi that members of the Chinese delegation ‘were very rude to the ambassador’ and exclaiming: ‘Extraordinary!’.

The police commander agreed, saying, ‘It was very rude and very undiplomatic I thought’.

It was not clear which members of the delegation they were referring to.

- BBC broadcast blanked out -

Beijing and Chinese state media at the time hailed the visit as a high watermark in Sino-British relations.

‘President Xi Jinping's state visit to Britain last year was very successful. Both sides have high level recognition of that,’ foreign ministry spokesman Lu Kang said on Wednesday.

Asked whether China had threatened to cancel the visit as mentioned by D'Orsi, Lu said: ‘I haven't heard of that scenario occurring’.

The BBC said a BBC World broadcast about the incident was blanked out in China.

Buckingham Palace said it would not comment on the queen's private conversations.

‘However the Chinese State Visit was extremely successful and all parties worked closely to ensure it proceeded smoothly,’ a palace official said.

Earlier on Tuesday, Cameron was overheard at another Buckingham Palace event calling Nigeria and Afghanistan ‘possibly the two most corrupt countries in the world’.

He was filmed making the remarks to the queen and Archbishop of Canterbury Justin Welby, ahead of an anti-corruption summit he is hosting in London on Thursday.

‘We've got some leaders of some fantastically corrupt countries coming to Britain,’ the prime minister said.

‘Nigeria and Afghanistan, possibly the two most corrupt countries in the world,’ he added.

Welby, who worked as an oil executive in West Africa before joining the church and who has also undertaken conflict resolution work in Nigeria, noted that ‘this particular president is actually not corrupt’.

‘He's really trying,’ Cameron agreed, and the queen noted to Welby: ‘He is trying, isn't he?’

It was not clear to whom they were referring, but Nigerian President Muhammadu Buhari and Afghanistan's President Ashraf Ghani are both due to attend the summit.

- 'Embarrassing' Cameron -

A spokesman for the Nigerian president said Cameron's comments on corruption were ‘embarrassing’.

‘This is embarrassing to us, to say the least, given the good work that the President is doing. The eyes of the world are on what is happening here,’ spokesman Garba Shehu said in remarks released on social media.

‘The prime minister must be looking at an old snapshot of Nigeria. Things are changing with corruption and everything else.’

Buhari has embarked on a widespread anti-corruption campaign since taking office one year ago, and is due to give a speech on the issue in London on Wednesday.

In Afghanistan, Ghani also made a promise to rein in runaway corruption when he was elected in 2014.

On Tuesday, a Downing Street spokeswoman said it would not comment on a private conversation, but noted that both Buhari and Ghani ‘have acknowledged the scale of the corruption challenge they face in their countries’.

She said that in a collection of essays to be published at the summit, Ghani writes that Afghanistan is ‘one of the most corrupt countries on Earth’.

Buhari, for his part, writes that corruption became a ‘way of life’ under ‘supposedly accountable democratic governments’, the spokeswoman said.

She concluded: ‘Both leaders have been invited to the summit because they are driving the fight against corruption in their countries.’