The independent elections watchdog is looking to change a code of conduct for political campaigners to stop them handling any completed postal votes.

It comes as it emerged police, in dialogue with the Crown Office, are continuing to assess allegations that pro-Union campaigners committed a criminal breach of electoral secrecy law by examining Scottish independence referendum postal ballot papers to gauge how well the Better Together campaign was doing before the polls had closed.

The Electoral Commission has circulated a consultation since September 19, the day after the referendum, revealing proposed code changes that "make clear campaigners should not handle any completed electoral registration, absent vote application forms or postal ballot packs".

While the proposals were not borne out of the referendum experience, sources say they expect any lessons to be learned from the poll to feed into the consultation.

Elections guidance on postal votes states it is already 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 law and liable on summary conviction to imprisonment for a term not exceeding 12 months and/or to a fine of up to £5,000.

Complaints about the referendum were passed to police by the public and the Commission after comments by Scottish Conser­vatives' leader Ruth Davidson and a prominent support of the Better Together campaign.

Ms Davidson said on television 45 minutes after the ballots closed that they had been "incredibly encouraged" by the results of a "sample opening" of the postal ballot, which, she said, had taken place around the country over the few weeks before the poll closed.

She said agents were able to "take tallies" of postal ballots "and the reports have been very positive for us".

The Commission's revised code of conduct, which focuses on behaviour in the lead-up to polling day, applies to candidates, their agents, staff and supporters and political party officers.

The revised code would tell campaigners they "should never touch or handle anyone else's ballot paper".

Campaigners are already told they should never observe voters completing their ballot paper as it should be completed "in secret".

The Commission said the revised code was embarked upon as its reviews revealed concerns from members of the public and electoral administrators about the impact of campaigners' activities "on vulnerable voters and on perceptions of the integrity of the absent voting process".

It found some voters felt pressured by campaigners to apply to vote by post and some expressed concerns over their role in handling postal vote applications and ballot packs while giving assistance to vote.

The Commission said: "We concluded it is not appropriate for campaigners to be directly involved in the voting process, including handling completed absent vote applications and postal ballot packs.

"We want to ensure campaigners are able to fulfil their vital role during elections.

"However, we are also clear that leaving unreformed the current involvement of campaigners in the voting process itself is not a satisfactory option."

The consultation document added: "Electoral fraud has the potential to affect the results of elections and undermine trust in the democratic process.

"Although there is no evidence to suggest there have been widespread, systematic attempts to undermine the electoral system in the UK, there is a consistent underlying level of concern among voters about electoral fraud in the UK."