'Referendums should be carried out in a way that promotes public confidence.

They should be credible, transparent and fair."

So says the Electoral Commission in its introduction to the first of 13 booklets setting out the rules for the independence vote. The watchdog adds: "Our objectives for referendums are: they should be well-run and produce results that are accepted; and that there should be integrity and transparency of campaign funding and spending."

No-one takes issue with those aims. It is essential that, when Scots take the most important decision about their country for 300 years, the result is accepted by all. It must not be open to challenge or tainted in any way by claims of malpractice or rule-breaking by either side in the campaign.

The Herald this week reported that one of the Electoral Commission's priorities, campaign spending, has become a cause for concern. With a number of campaign groups beginning to register as "permitted participants" before the spending rules kick in on May 30, fears were raised they might be used as front organisations to boost the main Yes Scotland or Better Together campaigns' spending power. If those fears are realised, the result might be questioned. The issue is as serious as that.

To recap, voices on the No side (as it happened) expressed concerns that if a large bunch of Yes-supporting groups were allowed to register as official campaigning bodies in their own right, the Electoral Commission might be landing itself with a difficult job policing the spending rules.

Under the rules, the lead campaigns Yes Scotland and Better Together can spend up to £1.5 million on leaflets, billboards, cinema adverts, events and anything else to win your vote in the final 16 weeks before polling day. Parties have their own spending limits, related to their number of MSPs, and other groups - obliged to register if they'll spend £10,000 - have a £150,000 cap.

So far two Yes groups, Business for Scotland and the Scottish Independence Convention, and a No group, the No Borders campaign, have been approved by the Electoral Commission. Christians for Independence has indicated its intention to register and National Collective, the "artists for independence" group are understood to have submitted forms.

But there are lots of other groups out there. Yes Scotland promotes no fewer than 16 "interest groups" - including Business for Scotland and Christians for Independence, together with Mums for Change, Cabbies for Yes, Eco Scots and others - on its website. Others, such as the Scottish Independence Convention and National Collective, are less directly linked, but clear links there are all the same. The convener of the Scottish Independence Convention, Elaine C Smith, is on the board of Yes Scotland, for example. On the other side, No Borders might be considered linked to Better Together because its backer, financier Malcolm Offord, has donated money to the Conservatives in the past.

Links between the main campaigns, pro-Yes or No interest groups and parties are not a problem. They are expected, inevitable even, and efforts to pretend they do not exist can only end in ridicule. The issue is whether these different bodies work together with the main campaigns when they are spending their funding. If they spend cash "as part of a common plan or arrangement", as the rules state, it counts towards the designated lead campaign's £1.5m.

How easy will that be to police? The Electoral Commission will monitor the media and investigate complaints. But with Better Together saying it will allow its own interest groups to register if a long list of Yes groups do, the task will be a big one.

Rules that are open to interpretation and the possibility of vexatious complaints would make it all the harder - and more time-consuming. The prospect of post-result disputes cannot be ruled out. On that, the pro-UK side feels it is on the back foot. Better Together insiders believe complaints about a narrow Yes win would be brushed aside as Scots embraced the enormity of their decision. Disputes about a No victory, by contrast, would be used for years to build support for a re-run.

Whether that view is fair or not, it would be better to avoid any doubts about the validity of result on September 18.