The period of "purdah", when Government announcements are put on hold during election campaigns, should be extended during the run-up to the referendum, it has been claimed.

The normal period of purdah before Westminster and Holyrood elections is 28 days and applies to all ministerial announcements, so the Government cannot be seen to be attempting to buy votes with new spending policies.

But Holyrood's Referendum Bill Committee has heard the traditional rules do not go far enough when it comes to the significance of the referendum campaign next year and that purdah should also be extended to a broader range of publicly funded agencies.

William Norton, a leading figure in the campaign against voting reform at Westminster, was critical of several aspects of the Referendum Bill, calling for a tightening of the purdah rules and casting doubt on the proposed "top down" approach to funding limits for next year's independence referendum.

Mr Norton said he had "high-level concerns" that the proposed purdah rule contained "loopholes and lacked an enforcement procedure". He said it "should be replaced by a measure with genuine teeth which also applies to bodies in receipt of EU funding".

His main concern was that purdah remained at 28 days and, crucially, applied only to the Government and not other publicly funded agencies.

That could leave it open, for example, for Historic Scotland to make announcements or organise events that could influence public opinion or sentiment in the run-up to the referendum.

He said a potential breach of purdah had not been dealt with during the voting reform referendum and the proposed rules for Scotland next year were even more lax.

Mr Norton insisted the Referendum Bill had a narrower scope, failing to cover grant-funded organisations that are not public bodies and creating "an obvious loophole for the misuse of public resources".

He said a campaign group or body wholly or mainly dependent upon taxpayers' money could support one side in the bill – which had managed to take existing purdah legislation and produce "something even less fit for purpose – and arguably creates an opportunity for the undue influence of the outcome".

Mr Norton called for the Electoral Commission to be relieved of any role in promoting the understanding of the independence question, arguing it would be dragged into the politics of the issue.

But despite Mr Norton's views, both Willie Sullivan, former head of Yes to Fairer Votes, and Professor Richard Wyn Jones of Cardiff University, both praised the proposals in the proposed bill as fairer than existing UK legislation.

Earlier, the Law Society of Scotland expressed concern that while the Scottish Government would be bound by statute to abide by purdah, the UK Government would not.

Director of law reform Michael Clancy said the UK Government made a commitment to observe the 28-day rule in the Edinburgh Agreement last year but any fallout for breaching this "would be more political than legal".

He explained later: "The Scottish Government would be subject to judicial review for any breach of the statutory duty for what it had done in that respect.

"The UK Government has to act reasonably but there would be no statutory obligation on it, so the consequences would be more political than legal."