Northern Rock's advisers and the tripartite banking regulation group of the Treasury, Bank of England and the Financial Services Authority yesterday told Olivant, the rival group, it would be treated on an equal footing with Virgin Group.
It is understood Olivant was ready to pull out of the auction, which is now a two-horse race, unless it secured the terms.
Virgin Group's consortium has effectively lost the "preferred bidder" status it was awarded three weeks ago. On the back of that development, Branson took out ads in UK daily newspapers in which he addressed a letter to Northern Rock customers.
Branson's letter thanked them for their support and although he admitted there was "still work to be done", he labelled Northern Rock as "ours".
He wrote: "I have the greatest respect for customers and I hope that you will continue to be a valued customer of our new and exciting bank."
The Virgin Money advertising account is currently up for grabs because incumbent Rainey Kelly Campbell Roalfe/Y&R resigned last week over the potential conflict with its Lloyds TSB account should Virgin land Northern Rock.
Olivant is led by Luqman Arnold, who was chief executive of Abbey National (now Abbey) in 2003 when it launched a high-profile rebranding campaign through TBWA\London, proclaiming Abbey was "turning banking on its head".
Yesterday, Northern Rock named its sales and marketing director Andy Kuipers as chief executive after Adam Applegarth elected to leave earlier than his agreed departure in February.