Energy Secretary Chris Huhne will learn tomorrow whether he will face charges for allegedly dodging a speeding penalty.
Director of Public Prosecutions Keir Starmer will make the announcement at 10am and will also announce a decision on Mr Huhne's ex-wife Vicky Pryce.
Prosecutors have recently received key emails in the case.
The Liberal Democrat minister has repeatedly denied any wrongdoing.
The decision comes shortly after the Sunday Times dropped its challenge to a court ruling ordering evidence to be disclosed. The material is believed to include exchanges between the newspaper's political editor and Mr Huhne's ex-wife.
Lawyers began reviewing the material, which relates to a speeding offence in March 2003, at the end of January after receiving it from Essex Police. An initial evidence file was delivered to the CPS last July.
Deputy Prime Minister Nick Clegg has warned that it would be a "very serious issue" if Huhne was charged.
He said in a recent interview that he and David Cameron would have to "take a view" if charges were brought against his Liberal Democrat colleague, adding that they were determined to uphold the "highest standards of probity" among ministers.
Mr Huhne will be told of the decision tomorrow morning shortly before it is announced publicly, said the CPS.