Prof Nick Fox, from the Institute of Neurology at University College London, said some of his patients had lost a fifth of some parts of their brain by the time they arrived at the clinic.

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But deputy PM Nick Clegg said Mr Fox had apologised to Parliament for blurring professional, political and personal boundaries and that the cabinet secretary was investigating the matter.

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The BBC's political editor Nick Robinson said the prime minister had given Mr Fox time to defend himself but the defence secretary had struggled to stem the tide of questions about his dealings with Mr Werritty.

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