An action group representing shareholders in Royal Bank of Scotland is planning legal action to recover losses sustained after they subscribed to a rights issue in 2008, shortly before the bank was nationalised.

A legal source with knowledge of the process said London law firm Bird & Bird will send a letter of claim to the bank today on behalf of a substantial group of shareholders.

A source at RBS said the bank had not received the letter or been served with proceedings.

Earlier, it was reported the claim would total £2.4 billion, on behalf of 7,400 private shareholders.

A senior source at a London wealth management institution said some of its private clients were taking part in the action.

Investors, represented by the RBoS Shareholders Action Group, are making the claim against the bank and a small group of former directors including Fred Goodwin, chief executive of the bank before it was rescued by the British taxpayer, legal sources said.

The claim centres on losses incurred by shareholders who subscribed to a rights issue, acquiring further shares in RBS at 200 pence in 2008. RBS shares currently trade at about 26 pence.

The action group has alleged on its website that the rights issue prospectus, published months before the company required a massive state bailout, was misleading.

"The group considers that it has substantial and credible legal and factual defences to the remaining and prospective claims, and will defend itself vigorously," RBS said in a statement today.

RBS sought to boost capital with a £12 billion rights issue in June 2008, offering more than 6 billion new shares to existing investors, who took up 95 per cent of the offer.

Later that year, the government acquired a majority stake in the bank and now holds more than 80 per cent of the shares.

The RBoS Shareholder Action Group did not respond to a request for comment.

Reuters