A civil servant sacked for leaking embarrassing disclosures is planning to launch a private prosecution against Redditch Labour MP Jacqui Smith accusing her of expenses fraud.
Ms Smith claimed £116,000 in second home allowance on her family home in Redditch while listing a London house she shared with her sister as her main home.
But Christopher Galley, a former Home Office official, claims the former Home Secretary was more often at the Worcestershire address. He said: "We are accusing her of fraud by misrepresentation of her second home allowance.
"We are suggesting that her main residence is in Redditch and not her sister's home in Peckham."
Mr Galley and Tory immigration spokesman Damian Green were arrested over leaks of Home Office documents but neither was charged. Mr Galley was then sacked from his job in April following a disciplinary hearing.
He has instructed Bark and Co solicitors and is to file a complaint with Westminster Magistrates' Court accusing Ms Smith of fraud by misrepresentation, he said.
Mr Galley, who is now research director of the Sunlight Centre for Open Politics, a pressure group, is also using the Freedom of Information Act to request details of Ms Smith's appointment diary.
Parliamentary Commissioner for Standards John Lyon is already investigating a complaint against her over her expenses. Ms Smith could not immediately be contacted for comment.
When details of her claims became public, she denied any wrongdoing. At the time she said: "I have tried to do what I think is the right thing for the taxpayer, for my ability to do my job as Home Secretary, for my family in terms of where they live. I think I have tried to do the right thing."
Last week she admitted her resignation six weeks ago was in part due to the scandal over her expenses claim for two pornographic films watched by her husband.