Alan Johnson will be investigated by the Electoral Commission following claims over donations to his deputy leadership campaign.
Last week the Sunday Mirror claimed student Waseem Siddiqui was used as proxy to pass more than £3,000 from his brother-in-law Ahmed Yar Mohammed, the treasurer of Croydon Central Labour Party, to the Health Secretary's failed deputy leadership bid.
The Labour MP was also accused of declaring four donations months late.
A spokesman for the Electoral Commission said the independent body was still waiting for an explanation as to why the money from Mr Mohammed was channelled through Mr Siddiqui.
Mr Johnson said he and his team had been 100 per cent honest and fulfilled its legal obligations in checking the source of Mr Siddiqi's cash.
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