An action group working on behalf of thousands of private investors has confirmed plans to pursue compensation amid fury at being “misled” by former RBS chief executive Sir Fred Goodwin and his colleagues.

Roger Lawson, of RBS Shareholders Group, said: “All the directors on the board at the time of the buyout will be targeted by this action.”

RBS is now 70% owned by the taxpayer following a government bailout a year ago after it lost a UK record £24.1bn in 2008.

Some shareholders claim to have lost more than £20,000. One investor, who did not want to be named, said she had lost “tens of thousands”, adding: “This is not just about getting our money back, this about sending a message to Sir Fred. It’s an utter disgrace he wasn’t sacked.”

The RBS action group’s potential claim will focus on “significant errors and omissions” made at the time of its £12bn sale of new stocks to existing shareholders in April last year, six months before the crisis. The call for investment was meant to strengthen the bank’s assets.

RBS’s balance sheet had been fatally weakened by its acquisition of Dutch bank ABN Amro under Sir Fred Goodwin.

Shareholders were asked to buy new shares at 200p each, with 95% of the stock being bought up.

But shares were hammered after the collapse of Wall Street banking giant Lehman Brothers and the government rescue of RBS, while the bank’s stock fell to an all-time low of 10p in January.

At an emergency meeting in London, Lawson said the action group would be looking to raise funds for legal advice on the strength of a potential claim.

He said he believed the prospectus issued at the time of the sale of the shares underestimated the risks facing RBS and “substantially misled” shareholders.

Although the justification for the issuing of new shares was to boost its finances, Lawson described it as a “bailout to fund [the bank’s] past mistakes”.

Meanwhile, Bradford & Bingley (B&B) shareholders are also planning a compensation claim. The shareholders accused the government of “legalised theft” as the failed bank’s valuer told them they may not receive news of any payouts until next summer.

Peter Clokey of PricewaterhouseCoopers, who will receive up to £4.8 million to calculate a compensation package from the government for B&B shareholders, said it would take up to a year to produce his results. But he said he did not want to “set any hares running” by predicting its final value.

The Treasury decided B&B was no longer a viable bank after the collapse in the share price, and a run on its deposits by customers.

The group’s savings business was sold to Spanish banking giant Santander.