The claim against the Edinburgh institution had been brought by US preference shareholders who filed a class action against RBS and its directors in 2009.

Among its claims were RBS did not fully disclose its exposure to sub-prime mortgages and gave an inaccurate assessment of its 2007 acquisition of ABN Amro.

In her judgement, Judge Deborah Batts wrote of RBS's stance on ABN Amro: "The statements that plaintiffs challenge ... amount to nothing more than corporate optimism."

She granted a request by RBS to dismiss the case against the bank and directors.

The decision comes as a group of UK shareholders are trying to raise funds to launch their own class action relating to the banks' £12 billion rights issue in 2008.