Britain's Barclays has conceded defeat in the seven-month battle for Dutch bank ABN AMRO, as rivals led by Royal Bank of Scotland move in to clinch the world's biggest bank takeover.

The result had been widely expected after a fall in Barclays' share price saw the value of its bid slip well behind the 71 billion euro ($100 billion), mostly-cash offer from the RBS consortium, which also includes Spain's Santander and Belgian-Dutch group Fortis.

Barclays said the merger protocol with ABN was now terminated, and that it was requesting payment of the 200 million euro break fee, which it said would significantly exceed the costs that Barclays incurred in connection with the offer.

The bank also said it would restart its buyback program, with up to 1.55 billion pounds ($3.16 billion) available to purchase a maximum of 196 million shares for cancellation.

The consortium is expected to announce the results of an ABN shareholder vote on its bid on Monday, and to declare its offer unconditional by the end of next week.