When the independence referendum takes place on September 18, however hard fought the campaign, however strongly feelings run on both sides, it is essential that the result is trusted and accepted on all sides.

That has been the mantra of both pro-independence and pro-UK supporters throughout the long campaign and rightly so.

The importance of this ballot to Scotland cannot be overstated. Whether it is Yes or No, it would be highly damaging to the country if the result were called into question because of doubts and recriminations around the methods used in achieving the winning vote.

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For that reason, Better Together's concerns about the way Electoral Commission rules might allow smaller pro-independence groups to be used as a means of boosting the main Yes campaign's spending power deserve serious scrutiny.

Under the rules, so-called permitted participants may spend up to £150,000 in the last 16 weeks before the vote; crucially, that sum does not count towards the £1.5m spending limits of Yes Scotland or Better Together as the lead campaigning bodies on each side, provided that those lead organisations and the permitted participants do not co-ordinate their activity or work together.

But who decides what amounts to co-ordinated activity and how is the Electoral Commission to police it? The rules are open to interpretation. They state that "the guiding principle is that, in all cases, you should make an honest assessment, based on the facts, whether you or another campaigner are spending money as part of a common plan or arrangement". Relying on honest self-assessment by campaigners is clearly risky; how is the Electoral Commission to establish firmly whether "informal discussions" have taken place (allowed) or whether two groups have agreed that they should cover particular areas, voters or arguments between them (not allowed)?

There is a genuine concern that it could prove to be impossible for the Electoral Commission and that if an inquiry were opened into the activities or one group or another due to concerns they were breaking the rules, it might be many months after the referendum result was declared before a definitive verdict was reached. Even if the rules were found to have been broken, it would be far too late to do anything about it.

Openness about who works with whom and where their money comes from is absolutely essential. The pro-independence groups understood to want permitted participant status have links with Yes Scotland. That does not mean they are co-ordinating activity but Better Together have a point to say it will be difficult to police the activities of such groups if a raft of them seek to register.

Better Together fears a "free-for-all" if all such groups are accepted, noting ominously that, in such circumstances, it "will have to respond".

That would be highly undesirable as it would create the clear danger of the referendum result becoming mired in controversy. It is up to the Electoral Commission to act to make sure that does not happen.