Sean Quinn and his family members will probably have to sue Anglo Irish Bank - and its ultimate owner the government - over the secret sale of 10% of the bank to the so-called 'golden circle' of 10 investors, former major stakeholders in the bank believe.

Big institutional shareholders, including the world's largest pension fund managers, are known to be monitoring the circumstances of the sale last July when Anglo arranged to sell about 75m shares, or 10% of the bank, to ten of its customers. Big institutions say they are poised to sue when the investigations into the apparent share-support transaction is complete.

Quinn would be forced to sue Anglo if he believed an illegal share support scheme had caused him and his family to endure large losses.

Now, major stakeholders believe that any findings of wrongdoing that emerge from official investigations will oblige the Quinn family, who between them owned 15% of the bank, to sue the bank. The family spent and lost up to €500m to buy shares in the bank after Sean Quinn lost at least €900m betting indirectly on Anglo shares through stock market bets, called contracts for difference, over 12 months.

A spokeswoman for the Quinns said on Friday the family had no comment to make on whether they planned to sue the bank over the 10% sale of shares in July.

Sean Quinn in an interview with RTE News in late January said he or his family had never been involved in "any impropriety" in their business dealings.

The Irish Association of Investment Mangers, whose members lost tens of millions of euro in the collapse of Anglo shares and its subsequent nationalisation, said they will be obliged to sue the bank to retrieve clients' money.

And big foreign institutional stakeholders, Invesco and Janus, will also be forced to sue after they lost €250m each following the collapse of the 7% stakes they owned in the bank. Big institutional shareholders believe that lawsuits are more likely to be successful because the bank is now owned by the government.

The Sunday Tribune has also learned that Morgan Stanley, which acted as a broker under the instruction of Anglo to buy the 10% stake last July has yet to be contacted by the Financial Regulator or the Office of the Director of Corporate En­forcement, which are investigating Anglo's affairs. A spokesman for Morgan Stanley in London said that the bank could not comment.

Credit Suisse, another large investment bank which acted as a counter-party to the Sean Quinn contracts for difference bets before last July, has also yet to be approached by Dublin investigators.