Elections watchdogs have ruled that the CBI's application to register as a supporter of a No vote in the Scottish independence referendum is void.

The Electoral Commission made the decision because the application from the business organisation to be a permitted participant had not been signed by a person authorised to do so.

Last week, CBI director general John Cridland said it had made an ''honest mistake'' in registering.

John McCormick, Electoral Commissioner for Scotland, said: "The law, and our own guidance, state who can sign a permitted participant application form.

"In this case, the CBI submitted a form to the Electoral Commission that had been signed by the wrong person and their application is void."

He added: "The Electoral Commission will meet shortly with the CBI to make sure they understand the campaigning rules at this referendum.

"We will monitor their activities over the 'referendum period' as part of the monitoring work we do ahead of any election or referendum."

When the CBI registered with the Commission to formally back a No vote last month, it said it had done so "in accordance with the law''.

But the move sparked a backlash that saw 18 bodies - including several Scottish universities, the BBC and broadcaster STV - either resign or suspend their membership of the business organisation.

Mr Cridland said today it was "now time to draw a line under this and focus on the issues".

A CBI spokesman said: "Following clear legal advice, an application to register under the terms of the Scottish Referendum Act 2013 has been declared void by the Electoral Commission as it was not signed by an authorised signatory."

He added: "The CBI is a politically independent and impartial body and will ensure that it complies with Electoral Commission guidance to safeguard its political independence.

"As businesses work hard to secure the economic recovery, the CBI has a job to do on behalf of its members and their employees to help create the right conditions for UK companies to grow and prosper, wherever they operate across the world. We will continue to do that without fear or favour."

Tony Banks, chairman of the pro-independence Business for Scotland organisation, said the CBI's reputation had been "fundamentally damaged".

Mr Banks said: "Registration is voluntary but the CBI has now been recognised by the Electoral Commission as an active participant in the campaign and will be monitored accordingly.

"The public expects all elements of the No Campaign to follow the law. The main issue is that CBI officials decided on a policy position against independence and began campaigning, including spending money, without a resolution of its membership. That is unlawful under Companies Law and a breach of the CBI's royal charter.

"The CBI's reputation has been fundamentally damaged. They have experienced a series of damaging resignations and that is set to continue. The CBI clearly does not represent business in Scotland."