The activist shareholder which spurred ABN Amro into holding merger talks with Barclays has thrown its weight behind a rival bidding group led by Royal Bank of Scotland, saying it is concerned that the pre-agreed sale of the Dutch bank's North American unit "unfairly hinders" the RBS consortium.

The Children's Investment Fund, a UK hedge fund with a stake of just under 3% in ABN Amro, said the bank's board should reveal the full details of its agreed €16bn ($21bn) sale of LaSalle Bank to Bank of America, after news of the disposal apparently caught RBS and its consortium partners by surprise.