Dr David Kelly, 59, went missing from his home near Abingdon, Oxfordshire, at around 3pm yesterday after telling his wife he was going for a walk, Thames Valley Police said.
The family called police when he had failed to return by 11.45pm last night.
Dr Kelly faced a grilling on Tuesday by MPs on the Foreign Affairs Committee about what he told BBC reporter Andrew Gilligan, who filed the original report claiming the Government had "sexed up" the weapons dossier.
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