Assael entered the list for the first time last year at number seven, but the 2007 list tells a different story. The west London practice dropped 34 places to number 41 as 91 new companies entered the list.
A spokeswoman said: 'While we might have dropped, the only other architect on the list also dropped and there were no new architects. There were 30 per cent more entries this year from last year.
'We are absolutely delighted. This consolidates our record as a top architectural employer, having also won the AJ100 Property Employer of the Year among other employer awards during 2006.'
Urban Splash, the Manchester-based property and regeneration developer, also had a bad year, plunging 57 places from number 25 to 82.
The only other architects on the list, BPTW Partnership, also fell to number 90 this year, 33 places lower than in 2006.