The IPCC said the three arrested were a 50-year-old sergeant who was arrested at work, a 29-year-old Pc arrested at an address in south London and a retired PC aged 48 who was arrested by appointment at a central London police station.
Sean Rigg died from a cardiac arrest at Brixton police station in August 2008 and the inquest jury found that police officers used "unsuitable" force after arresting the 40-year-old schizophrenic for attacking passers-by and police officers in Balham, south London.
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The Labour leader did not say whether he would maintain Britain's nuclear deterrent programme.
Ukip leader Paul Nuttall also said he would want to get rid of Sharia courts.
Over 40,000 people picked up their packs to take part in the annual marathon in the capital.