Zurich UK Commercial sent support packs to 10,000 brokers this week to explain its latest price increases - the most significant being employers' liability with a rate hike in excess of 50%.
They have also announced an average price rise of approximately 25% in property and up to 10% rises in motor.
The packs highlight 15 external factors, which the company says has forced it and the rest of the market to raise prices in these sectors.
These include retrospective legislation, claims inflation and industry levies, together with a lower interest rate environment and falling equity levels.
Distribution and marketing manager David Smith said: "It is difficult for insurance customers to understand why premiums are rising. What we want to do is provide our brokers with information so they can articulate to clients early, why the prices have to rise. There is more pain to come and clients need to budget for the increased prices and begin to take an active interest in managing risk."