Amlin's pre-tax profit leapt 17% in the six months ended 30 June, while its combined ratio fell below 80%.
Announcing its half-year results, Amlin reported a pre-tax profit of £74.2m, compared to £63.3m for the same period of 2003.
Its combined ratio improved ten points to 73%, while gross written premium increased by around 7% to £709.7m.
Amlin said renewal rates across the insurer's portfolio for the first half had shown a modest average reduction of 2.5% from 2003 levels.
It added it would be paying an interim dividend of 3p per share, compared to 0.85p for 2003. Commenting on the dividend, chief executive Charles Philipps said that the insurer would be paying out 30% of its distributable earnings over the full year.
The insurer said it continued to experience "a relatively benign claims environment", aided by the ruling in the Silverstein trial that the World Trade Center terrorist attack was a single event.
An Amlin statement said: "With the exception of aviation-related claims, Amlin's losses from this tragic event are now well developed and uncertainty surrounding the losses has diminished."
The insurer confirmed that the capacity of Syndicate 2001 would be reduced by £150m to £850m in 2005.
