Deloitte and Touche Wealth Management has been fined by the Financial Services Authority (FSA).
The FSA said it imposed the £750,000 fine for Deloitte's failure to keep proper records and carry out a review of pensions mis-selling on time.
The finance watchdog said the group was 54 months late in dealing with some claims of pensions mis-selling.
It added that the group had failed to keep sufficient records in 96.8% of the client files it had looked at.