The Financial Conduct Authority said two of the 26 industry firms reviewed had been "referred to enforcement in specific cases where the FCA identified potential rule breaches".
On whether the review had prompted any improvement in behaviour, the regulator said that "many" firms had "changed their arrangements", adding later that this applied to "most" firms.
The FCA, led by Martin Wheatley, said it had found evidence of both life insurance and advisory firms bypassing the retail distribution review (RDR) reforms which took effect at the start of 2013.
It said: "The changes we made to the retail investment advice sector were designed to mark a step change in the way advice was given. It signalled the end of advice that might be influenced by the commission payments made by product providers to advisory firms, and the start of a new era of trust and transparency between a firm and its customers. The findings of this review reveal that the actions of some firms have the effect of undermining the objectives of the RDR."
The regulator uncovered potential conflicts of interest in long-term agreements between advisers and providers, such as guaranteed places for insurers on advisers' panels, and in gifts, promotional competition prizes, joint marketing initiatives and promotion. The FCA found firms taking an "overly broad" interpretation of the rules to justify a wide range of benefits.
It is also concerned about the survival of excessive hospitality, citing instances of advisers taking multi-day overseas trips with spouses or family which were paid for in large part by providers.
Further examples of payments by insurers which "appeared to be linked to securing sales of their products" included an increase in spending on support services such as research or management information, IT upgrades, and payments to advisers for management team meetings.
"Further, the FCA identified that certain joint ventures, where a new investment proposition is jointly designed by providers and advisory firms, could create conflicts of interest and potentially lead to biased advice."
Asked to comment on the review and on whether their practices included "soft commissions", some Scottish insurers were reticent on detail. A Scottish Widows spokesman said: "I can confirm that we are not one of the companies that has been referred."
Hugh McKee, chief executive at Scottish Life, Bright Grey and Scottish Provident, said: "We worked closely with FCA through the course of the thematic review. It is in the interests of all parties, providers, advisers and their customers alike, that there is clarity around what constitutes good practice in the provision of services to financial advisers."
Standard Life said: "Standard Life does not use soft commission. In a small number of instances we provide payments for attending training or for advertising that are allowed within the rules and guidelines of the FCA."
A spokesman for Aegon said: "There are circumstances where payments from providers to advisers can improve consumer outcomes without creating any bias, for example, training on the features of our products that will benefit their customers. Aegon has made payments in the past where we are satisfied they meet our understanding of the criteria. We will of course review our understanding in light of FCA further clarification."