BETTER Together's place in the referendum campaign was last night thrown into confusion, after it emerged its official application to take part contained the wrong address.

The pro-Union movement gave its Glasgow HQ as its address when it applied in April to become a "permitted participant" in the referendum.

However, because it is a limited company, the law says Better Together should have used its registered office address in Edinburgh.

Better Together said it had been acting on the Electoral Commission's advice, and that the watchdog told it to use the Glasgow address because this was its day-to-day campaign base.

The Commission initially told the Sunday Herald a wrong address would render an application "invalid", and prompt a fresh application.

However, when the specifics of Better Together's case were put to it, the Commission said there was "no problem" with the application after all.

If the application was invalid, it would cast doubt on the No campaign's legitimacy.

The Commission admitted it had checked Better Together's address and found the correct one was in Edinburgh, but rather than asking Better Together to amend it, the Commission had simply recorded the Edinburgh address on its own "internal approval record" and used it as the basis for processing the application.

The Commission last night updated its online register of campaigners to show Better Together's Edinburgh address, and blamed an "administrative error" for not doing so sooner.

Earlier this year, the Commission ruled the CBI's application to be a campaigner was "void" because it was signed by the wrong person, a breach of the same law which says Better Together should have used its Edinburgh address. Despite the inaccuracy, the Commission insisted Better Together's application was valid and consistent with its guidance and "the law".

However, the Commission was unable to say if the application complied with the relevant section of the Scottish Independence Referendum Act 2013, which is the critical law involved.

A Yes campaign source said: "This suggests real uncertainty and confusion about the exact status of the No campaign, and whether or not they have adhered to their legal obligations. It does indicate a lack of basic competence, which is embarrassing to say the least and could yet be a factor which influences the result."

There are almost 30 registered campaigners in the referendum, including individuals, unions and political parties, as well as Better Together and Yes Scotland.

Under electoral law, companies "must" declare their full company name, their office registered with Companies House, and their company number when applying to be a permitted participant. Better Together, whose full legal name is Better Together 2012 Limited, should therefore have used its registered office address.

Since its creation in June 2012, this has been 133 Fountainbridge, Edinburgh, the same office as its lawyers, Tods Murray LLP. Instead, it used 5 Blythswood Square, Glasgow.

After the Sunday Herald discovered the error, it asked the Commission in general terms about the consequences of an inaccurate address on a form to be a referendum permitted participant.

In a statement on Thursday, the Commission said: "If an organisation or individual provided inaccurate information on their form and notified the Electoral Commission of that, their application would be invalid and we would work with them to make sure they supply an application with the correct information."

However, when we raised Better Together's address on Friday, the Commission said: "It doesn't impact on Better Together's registration at all and there was no problem with the information they provided us."

In statement yesterday, the Commission said: "The approval of an application by Better Together to register as a permitted participant was consistent with our guidance and the law. Their registration ... is valid.

"Following Better Together's application ... we verified their details, including checking their details on Companies House. This is a straightforward and standard practice that we carry out with all applications. It would not have required any correspondence with Better Together. Better Together's address with Companies House was in Edinburgh.

"This address should have been recorded on our list of permitted participants rather than the Glasgow address. This was an administrative error on our part and has been amended accordingly on our website."

A Better Together spokesman said: "We followed the guidance and advice given to us by the Electoral Commission. They have made clear to us that there was an administrative error on their part and has been rectified."