Richard Rogers Partnership and Grimshaw have this summer reported sharp falls in annual pre-tax profit. It was disclosed in February that Foster and Partners had turned in disappointing results.
RIBA president George Ferguson said that practices exposed to the international market for signature projects were more likely to have been affected by the attacks on the World Trade Centre and the Pentagon than those working primarily in Britain.
He said: "There was a lot of nervousness over investment after 9/11. It was probably tougher on the international scene than the national one."
RRP made a pre-tax profit of £326,000 for the 12 months to 30 June 2002, a fall of £340,000. Turnover rose £100,000 to £15.07m.
Marco Goldschmied, managing director of RRP, said the terrorist attacks on 11 September 2001 had hit the firm's results, and noted: "If there is a downturn this year, it will be because of the Iraq war."
Goldschmied added that pre-tax profit was in fact about £125,000 more than the reported figure, but RRP had taken a conservative estimate of how much one large client would pay of its fee. RRP has since received full payment.
If there is a downturn this year it will be because of the war in Iraq
Marco Goldschmied of RRP
Grimshaw announced a pre-tax profit of £108,000 for the 12 months to 31 October 2002, a drop from £405,000 the previous year. Turnover also fell, from £8.71m to £7.21m. Christopher Nash, managing director of Grimshaw, declined to comment on the result.
Foster and Partners' announced earlier this year that it had made a pre-tax profit of £1.7m for the 12 months to 30 April 2002, a fall from £3.5m in 2001.
At the time, a spokesperson for Foster said: "There was a downturn as well as a knock-on effect from the events of 11 September."
Grimshaw last month refused to certify practical completion on its highest-profile project, the £23m Bath Spa complex. The lottery-funded enterprise, which is being built by Mowlem, is 50% over budget and almost nine months late. Sources close to the project believe it will be finished in October.