(Reuters) — A small group of Royal Bank of Scotland retail shareholders is close to joining three other investor parties and settling a £4.0 billion ($5.03 billion)-plus lawsuit against the bank out of court.

State-controlled RBS offered five investor groups £800 million ($1.01 billion) last week in an effort to draw a line under allegations that it misled shareholders during a £12 billion ($15.09 billion) fundraising at the height of the financial crisis in 2008.

One industry source familiar with the situation said he expected a formal announcement over the next few days that the small retail shareholder group, led by lawyer Leon Kaye, would become the fourth group to accept the offer. Three institutional investor parties agreed to the RBS offer last week.

This would leave the RBoS Shareholder Action Group the last claimants still considering whether to take the cash on offer or proceed to trial in one of the largest and most complex lawsuits in English legal history.

"The Action Group notes that the Leon Kaye Group, representing 0.6% of the claimants by value, has indicated its agreement in principle with RBS's offer," a spokesman for the group said. "We are considering our position with RBS and its advisers."

RBS said in a statement it was pleased to have settled with some claimants and was hopeful of settling with the remaining groups.

The RBoS Shareholder Action group, which represents around 27,000 retail investors and more than 100 institutions, including Bank of America Merrill Lynch and Aberdeen Asset Management, says its claim is worth around £1.8 billion ($2.26 billion), including interest and costs.

It is the only claimant group to pursue both the bank and former directors over alleged recklessly optimistic statements that gave a "grossly misleading impression" about the bank's financial health in 2008.

RBS Chief Executive Ross McEwan has said he is worried about the damage a trial could inflict on the bank's battered reputation. But he also said RBS could not agree to a deal that was unfair to shareholders.

The case has cast a long shadow over the Edinburgh bank, which remains 73% state-owned since it was rescued in a £45 billion ($56.58 billion) bailout.

A six-month trial to establish liability has been scheduled for next March. A second trial to establish any damages will follow. RBS, which has already run up a legal bill of more than £90 million ($113.2 million), has said the case may not be settled before 2023 if it goes to trial.