POLICE Scotland have passed on "information" to the Crown Office having concluded a year-long investigation into allegations pro-Union campaigners breached electoral secrecy laws during the Scottish independence referendum.

The development comes nearly a year after police were instructed to launch an official probe over complaints surrounding comments made by Scottish Conservative leader Ruth Davidson that postal vote "tallies" were being taken in the weeks before the referendum ballot closed at 10pm on September 18.

On televised coverage of the referendum results, 45 minutes after the polls closed, Ms Davidson said that the Better Together camp had been "incredibly encouraged" by the results of a "sample opening" of the postal ballot that she said had taken place around the country over the few weeks prior to the poll.

United front flashback: From left, Johann Lamont, Alistair Darling, Ruth Davidson and Willie

Complaints over her account of the postal vote "tallies" raised concerns the information may have helped inform the No campaign's decision to issue the "vow" of more powers for Scotland from the three main party leaders.

Police Scotland has confirmed that they have now completed their investigation which was launched after the Crown Office instructed that there should be a formal probe following the complaints.

The Herald revealed that police twice spoke to Scottish Conservative leader Ruth Davidson as a potential witness over comments she made that the "tallies" were being taken in the weeks before the referendum ballot closed at 10pm on September 18 last year.

It is understood no arrests have yet been made and there are no outstanding warrants.

A Police Scotland spokesman said: "Police Scotland has completed enquiries and the matter now rests with the Crown Office and Procurator Fiscal Service."

A Crown Office spokesman added: “The Crown Office has received information regarding the investigation carried out by Police Scotland and will consider if further action is necessary.”

Political agents and campaigners are allowed to oversee the postal vote opening sessions, where checks are made to verify the signatures and dates of birth on postal voting statements against computerised records.

However, Elections Scotland instructions on postal votes in advance of the referendum stated that it is "an offence for anyone attending the opening of postal votes to attempt to ascertain how any vote has been cast or to communicate any such information obtained".

Failure to observe the secrecy requirement is a criminal offence punishable by up to 12 months in prison and/or to a fine of up to £5,000.

Guidance provided to electoral administrators and returning officers for the General Election, as a result of the experience of the referendum, were warned to keep the postal ballot secret and told that voting tallies by political agents is illegal.

Mary Pitcaithly, convener of the Electoral Management Board for Scotland recommended to returning officers in Scotland that they take particular care in making sure the law was complied with during the General Election and that the secrecy requirement was explained to all those attending postal vote openings.

The moves which the EMB said "draw on lessons learned from the Scottish independence referendum" include asking that ballot papers are handled face down so that no mark on the front of the paper is able to be seen by observers.

The postal vote, made up between 20% and 50% of the counted votes. Around 800,000 people, or 19% of participants, voted by post in the referendum.

The Electoral Commission has also advised all electoral administrators that the law prohibits tallying at postal vote opening sessions.

The advice states that under the Section 66(4)(d) of the Representation of the People Act 1983 it is "not permissible to attempt to ascertain the candidate for whom any vote is given in any particular ballot paper or communicate that information.

"This provision therefore prevents those present at the postal vote opening from attempting to ascertain the way individual ballot papers are marked."

Police have refused over the year of the investigation to comment on what progress they have made.

Some complainers raised concern that no police action had been taken in advance of the General Election.

Video footage of Ms Davidson talking about the ballot viewing was forwarded to both the police and the Electoral Commission.

In televised coverage she says: "Postal votes are going to be enormously important in this campaign; about 18 per cent of the vote is going to come out of postal ballots and we have had people at every sample opening, around the country, over the last few weeks, while that's been coming in. And we've been incredibly encouraged by the results."

Later, referring to postal ballots, she said: "Different local authorities have had openings around the country", adding, "there's people in the room that have been sampling those ballot boxes that have been opened and have been taking tallies and the reports have been very positive for us".