The video proof that Cameron DID talk to schoolboy, 16, with hangover

The Tory leader sparked controversy by retelling the story – swearing included – in his party conference speech.

Mr Cameron's account of his exchange with the unnamed 16-year-old was greeted with scepticism when the governors at the school – which he did not identify – questioned his version. Governors at Kingswood Arts College in Hull, where Mr Cameron spent two days 'teaching' last May, said they knew of no pupil who had boasted to Mr Cameron of being 'p*****'.

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Nor did they recognise his account of how a teacher had told of his astonishment that the boy had trashed a room and attacked a member of staff – and yet had not been expelled.

However, The Mail on Sunday has obtained video proof that Mr Cameron was telling the truth about his chance meeting with the boy in a corridor. Although the sound quality is poor, the key parts of the conversation can be heard.

Mr Cameron starts by saying: "What exam are you doing?" The boy replies: "I don't really know."

Cameron: "You don't really know?" A teacher interjects: "I have just this second told you. Preparation for languages."

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Teacher to Cameron: "He has got himself...there are better sides to him."

Cameron: "Why are you knackered?"

Boy: "Got p***** last night."

Cameron: "Yep. Good luck."

The video of Mr Cameron's trip to the school also shows him chatting to three teachers in a school office after his conversation with the hungover pupil.

A teacher says: "Look at that child [names hungover boy]. I taught him in year nine.

"Do you remember the last week of the term he went berserk in our department?

"He threw a table at a teacher, bit [names individual] and spat at teachers.

"He was like a feral animal. Now that kid got five days' exclusion given to him not at the end of term, but five days had to be served at the beginning of the term." Cameron replied: "So a complete delay."

Mr Cameron's description when he addressed the Tory conference in Blackpool went as follows: "I stopped a boy as he was running into his GCSE exam.

I said, "What's the problem?" and he said, "Well, I got completely p***** last night, I have got a hangover and I'm going to flunk this exam."

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"I asked a teacher about him and I was told that he had attacked a teacher and trashed a classroom and none of us know why he is still in this school."

Last night the boy recalled: "We had been drinking diesels, which is a mixture of lager, cider and blackcurrant.

"I felt so rough the next morning that I wasn't going to go to the exam but my mum dragged me out of bed. "I remember standing in a doorway when this bloke walked past with a camera filming him.

"I did not know who it was. He asked me what exam I was doing and I could not remember.

"I just knew that I had one. I told him I had been on the p*** but I don't remember much else about it."

He took just two GCSEs in PE and media studies and left the school this summer.

"I don't know how I got on because I've not bothered to pick up my results yet," he said.

"I've had a couple of jobs since.

"I packed chickens at a factory in Doncaster for a day but that wasn't for me and I went to do a cleaning job but the agency sent me to the wrong place: I was in Hull when I should have been in Ireland."

Recalling the time he bit the teacher, he said: "I wanted to leave the class so I was being mouthy. I started kicking off, throwing chairs about. "When he got me outside the classroom he put his arm round my throat. I was panicking at being restrained and I just bit him. I know it drew blood."

By the time he came to year ten he was a part-time student, studying just three subjects.

"The only subject I really liked was PE," he said.

"I enjoyed history but after I bit the teacher in year nine, we really fell out. It was like a bonus being thrown out because it meant I could go and hang out with my mates." His mother, an office worker, 38, said he suffered from claustrophobia and was upset that the video clip had been posted on YouTube.

"To call him a feral animal is disgusting," she said.

The boy now hopes to have a career in the Army.