The practice has recorded a slump of £647,590 in its profits last year, from £1,267,363 in 2005 down to £619,773 the following year.
As the figures suggest, the practice has undergone some significant changes from 2005 to 2006.
According to the practice, the profit dropped due to a management buyout in 2006, which saw the other eight directors buying shares from John McAslan, who remains majority shareholder with 47.5 per cent.
A spokeswoman said: 'We went through some significant changes in 2006, and we pumped a lot more money into the business, with a lot of our projects actually being on site.
'We are confident we will return to the normal figure in 2007.'
Last week, the practice announced it had won planning and secured listed building consent for its £400 million King's Cross Station redevelopment.
McAslan is also leading the £350 million reworking of Birmingham New Street Station, which is yet to go in for planning.