Police have handed over evidence about Peter Hain's campaign donations to the Crown Prosecution Service (CPS).
The CPS will now decide if there is a basis for prosecution.
Last week it was revealed Mr Hain, former work and pensions secretary, had been interviewed by police over his failure to register political donations.
The interview occurred weeks ago, with officers investigating details of his campaign to be deputy Labour leader.
It is alleged he failed to declare £103,000 to the Electoral Commission.
The money was declared four months after the end of his campaign, way past the 30-day requirement for donations over £1,000.
The £103,000 figure constitutes 17 different donations. Mr Hain went to the Electoral Commission in January with details of the donations, five of which came through a seemingly functionless thinktank called the Progressive policy Forum.
Wendy Alexander, Labour's leader in Scotland, recently resigned over less serious allegations which Hollyrood's standards committee thought significant enough to impose a one-day ban from the Scottish parliament.