Northern Rock said it did not consider such action "to be warranted or appropriate" but if necessary it would convene a meeting.
Shareholders were told they need to accept a deal or risk the bank going into administration, people familiar with the situation have said. Virgin is also not proposing a break-up.
VIRGIN PLAN
Branson, one of the world's highest-profile businessmen and estimated to be Britain's 11th richest person with a 3.1 billion pound fortune, said he is not planning any material cuts to Northern Rock's 6,000 staff and will keep its Newcastle base.
The bank will be renamed Virgin Money, keep a stock market listing, rebuild a deposit base and have financial flexibility.
"We will achieve all this without additional burden on the taxpayer and we will offer shareholders the opportunity to participate in the future growth of the business," Branson said in a letter to Northern Rock's customers.
The Virgin consortium will hold no more than 55 percent of the enlarged group if the underwritten rights issue of shares is fully taken up.
Brian Pitman, who was chairman and chief executive of Lloyds TSB and regarded as the most influential British banker of the 1990s, would be chairman of the enlarged Virgin Money.
Jayne-Anne Gadhia, Virgin Money's chief executive, would have the same position at the enlarged group, advised by George Mathewson, former chairman and CEO of Royal Bank of Scotland and architect of deals including the NatWest takeover.
U.S. insurance giant AIG, which had been named as part of Virgin's initial consortium, will offer credit insurance to help raise debt, but it is not putting in equity.
Northern Rock said its board will continue to explore other options as part of its strategic review.
U.S. buyout firm J.C. Flowers was regarded as the nearest rival to Virgin in getting backing. Other potential suitors include investment firm Olivant, backed by former Abbey National chief executive Luqman Arnold, and Cerberus, another U.S. buyout firm, in tandem with U.S. finance firm GMAC.
Northern Rock is being advised by Merrill Lynch, Citigroup and Blackstone. Virgin's advisers are Greenhill and New Boathouse Capital, part of Quayle Munro.
