NatWest Bank has been fined a total of £750,000 by industry regulators the PIA and Imro for rulebook breaches.
The bank must also pay £2.35m in compensation to about 4,500 investors for failing to give agreed discounts.
The PIA fined NatWest £500,000 for compliance failings which were discovered during monitoring visits in 1997, including a failure to monitor investment staff and to assess risks adequately.
The regulator also found NatWest did not have appropriate training, did not properly assess the competence of its regulated salesforce and often failed to produce adequate reasons-why letters specifying reasons for transactions.
Imro fined NatWest £250,000 for breaches of rules in the running of its unit trust business between Jan uary 1993 and June 1999.
The regulator says the bank failed to give agreed discounts to investors and to carry out regular reviews of investments held in customer portfolios to ensure they performed in line with the other portfolios managed by NatWest.
Banking ombudsman David Thomas has criticised banks for misselling endowment mortgages, saying he has “seen cases where customers were clearly given misleading advice”.