Two men and three women have been arrested as part of a crackdown by the financial regulator over insider dealing and market abuse.
Raids were carried out at at properties in London, Lincolnshire, Leicestershire and North Yorkshire. Those arrested were aged between 37 and 63.
The FSA has so far secured 21 convictions for insider dealing and has stepped up its efforts to tackle market abuse over the past few years.
The latest arrests are not linked to any other ongoing insider dealing probes.
The Financial Services Authority (FSA) has today published figures showing that complaints to financial services firms have increased by 59% - largely driven by Payment Protection Insurance.
The main trends in the figures, reported in the first-half of this year, are:
- Complaints about general insurance and pure protection increased by 99% to 2,541,430;
- Within this product group, payment protection insurance accounted for 2,232,294 of those complaints, an increase of 129%;
- The number of banking complaints increased by 5% to 828,040;
- Within this product group, complaints about current accounts dropped by 13%.
Some companies have claimed the rising fees required to service the product after interest rates fell in 2008 have forced them out of business.
The City watchdog is expected to confirm that banks are writing to customers who have taken an Irsa and an independent assessor will look at the most complicated cases and determine whether compensation should be paid.
The claims echo the payment protection insurance (PPI) scandal that emerged last year, costing banks billions of pounds, and come in the week Barclays was fined £290 million for manipulating interest rates.
Britain's banks will be embroiled in a fresh scandal today over complex financial products which have landed small businesses with spiralling bills.
The Financial Services Authority (FSA) is expected to reveal that it has found evidence of mis-selling as part of a review into the way lenders pushed so-called interest rate swap arrangements (Irsas).
Irsas are complicated derivatives products that may have been sold as protection - or to act as a hedge - against a rise in interest rates without the customer fully grasping the downside risks.