Singer will pay Knight Williams £5m up front and a further £12m, much of which will go to settling the complaints.
Precise figures for client compensation will emerge only after detailed negotiations, but sources close to the talks expect millions of pounds to be paid out by Knight Williams to the pensioners affected.
Tony Fraher, chief executive of Singer & Friedlander Investment Funds, stressed that the bank was buying only the right to manage £400m of funds. It is not buying any company assets or liabilities, or the independent financial adviser arm of Knight Williams, which will now devote itself to processing the complaints in association with the Securities and Investments Board and the supervising accountants, Ernst & Young.
The proposed acquisition follows 15 months of campaigning by the 350- strong Knight Williams Investors Action Group. Its complaints against the independent financial adviser concern high charges, poor returns and inappropriate products. Knight Williams has been one of Britain's biggest independent financial advisers, with 24,000 clients and £500m under management.
Kenneth Jordan, who founded the group with his wife, Dilys, welcomed the news: "We're very pleased. We're not there yet but we're nearly there. We are most grateful to all the MPs and the press who have supported us."
As part of the deal, Singer will cut annual management charges by 40 per cent, which could represent an average saving of £200 a year on a £20,000 holding.
This will include reducing the 2.5 per cent charge on cash funds to 0.5 per cent, to 1 per cent for bond funds and to 1.5 per cent for other funds.
Once the deal goes through the funds managed by Knight Williams will be dissolved and the assets will transfer to Singer's range of investment funds. Investors will receive shares in Singers' funds in allocations chosen to match, as closely as reasonably possible, the existing asset allocation and risk profile of each Knight Williams fund, according to the merchant bank.
Last year the action group secured an agreement that the SIB would deal directly with the complaints, after dissatisfaction with the previous IFA regulator, Fimbra. All complaints will be supervised by Ernst & Young and referred to the SIB if need be.
"It is important that there was an independent monitor to oversee the complaints procedure," said Mr Jordan, explaining E&Y's involvement.