Wellington Underwriting reported a massive £69.3m pre-tax loss for last year.
The result, down from a profit of £4.4m for 2000, includes a charge of £73.4m from the 11 September attacks.
Wellington has scrapped its final dividend for shareholders. Its huge World Trade Centre (WTC) loss comes from its exposure to aviation and US property risks and to catastrophe reinsurance.
Its Lloyd's syndicate 2020, which is managed by a subsidiary, drives much of the group's performance.
It wrote gross premiums of £868m last year and incurred net losses of £415m, with a combined ratio of 143%.
The combined ratio shows claims and costs as a percentage of premiums.
The cost of the WTC attacks was concentrated on Wellington's non-marine and reinsurance divisions, although no part of the business escaped unscathed.
The group estimated its gross cost of the terrorist attacks at £267m before reinsurance and £73m net of reinsurance.
It was also hit badly by the downturn in stock markets. Its return on equity last year of dropped by 45.1% producing a loss after tax of £46.1m.
