The footage has never been found, perhaps because, in the carefree spirit of the meeting, no film was ever put in the camera.

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The campaigner said he had taken the secret camera along to the meeting in July in the hope of catching Mr Duncan out but he regretted getting him into trouble because he was a "very charming and generous guy".

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Meeting in 2011, they decided to create a new kind of motion-controlled camera.

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