Section 5. (a) Rates shall be made in accordance with the following provisions:—

1. Manual, minimum, class rates, rating schedules or rating plans, shall be made and adopted, except in the case of specific inland marine rates on risks specially rated, and except in the case of special rates on other than inland marine risks where manual, minimum, class rates, rating schedules or rating plans are not readily available.

2. Rates shall not be excessive, inadequate or unfairly discriminatory.

3. Due consideration shall be given to past and prospective loss experience within and outside this commonwealth, to the conflagration and catastrophe hazards, to a reasonable margin for underwriting profit and contingencies, to dividends, savings or unabsorbed premium deposits allowed or returned by insurers to their policyholders, members or subscribers, to past and prospective expenses both countrywide and those specially applicable to this commonwealth, and to all other relevant factors within and outside this commonwealth; and in the case of fire insurance rates consideration shall be given to the experience of the fire insurance business during a period of not less than the most recent five-year period for which such experience is available. In considering catastrophe hazards with respect to homeowners insurance rates, the commissioner shall consider catastrophe reinsurance and factors relating thereto.

(b) Except to the extent necessary to meet the provisions of subdivision 2 of subsection (a) of this section, uniformity among insurers in any matters within the scope of this section is neither required nor prohibited.

(c) Rates made in accordance with this section may be used subject to this chapter.

(d) Nothing in this chapter shall abridge or restrict the freedom of contract between insurers and agents or brokers with respect to commissions or between insurers and their employees with respect to compensation.

(e) Two or more insurers who by virtue of their business associations in the United States represent themselves to be or are customarily known as an ''insurance company group'', or similar insurance trade designation, shall have the right to make the same filings or to use the same rates for each such insurer subject to subdivisions 1, 2 and 3 of subsection (a) of this section; and nothing contained in this chapter shall be construed to prohibit an agreement to make the same filings or use the same rates and concerted action in connection with such filings or rates by such insurers. This subsection shall not apply to two or more insurers who are not under the same common executive or general management or control and who act in concert in underwriting groups or pools.