The consortium now has until 23 July to make a formal offer

Rival bidder Barclays has also been given until 23 July to table an offer.

Both bidders are waiting for the Dutch Supreme Court to rule on whether ABN is allowed to sell its US bank LaSalle without getting shareholder approval.

The offer made by RBS and it partners, Spain's Santander and Belgium's Fortis, is dependant on LaSalle not being sold.

ABN has backed a 62.8bn euro ($85.3bn; �42.5bn) offer from Barclays, and plans to sell LaSalle to Bank of America for $21bn as part of the deal.

However, a group of ABN shareholders have tried to block the sale, saying it is not in their best interests and is only being done to block RBS, which has tabled a higher 71.2bn euro offer.

The Commercial Court ruled in favour of the shareholders' group, but the Advocate General disagreed.