PKF, which was reported to have been in talks about being taken over by rival BDO this summer, saw turnover tumble from £108.4 million in 2011 to £103.3m in the 12 months to March 31, 2012.
Pre-tax profit dropped by £2.6m to £13.7m, according to accounts filed by PKF (UK) at Companies House.
In its report to the members, PKF said: "The country is still in an extended downturn and this continues to have a significant effect on the accountancy and business advisory sector."
The average profit for each of the partnership's 70 members plunged to £188,000 from £207,600 in 2011 when there were 75 members.
However, the share of profits allocated after the year end to the member with the largest entitlement was £570,000, up 17.5% on the £485,000 paid out in 2011.
The firm is headed by Richard Bint, who became senior partner in April 2011 having has been with the firm since joining as a student accountant in 1975.
PKF cut the number of members and staff from an average 1324 in 2011 to 1279 in 2012.
Staff costs at the company dropped from £54.1m to £52.5m.
The vast bulk, some £45.7m, of PKF's revenue came from assurance and advisory services, where income was flat on the previous year.
Its second-largest segment was taxation and financial planning where turnover fell from £22.4m to £21.7m.
Management consulting accounted for £16.8m of income, down from £19m. Corporate recovery dropped from £12.1m to £10.7m.
Meanwhile, corporate finance and forensic work fell from £9.3m to £8.5m.
The UK was the dominant territory for PKF accounting for 92.5% of income.