Analysis contained in the Share Centre's Profit Watch UK quarterly bulletin, which focuses on the country's 350 largest listed companies, concluded that profits after tax for the year to the end of March dropped 33.8%.
The report, which covered the 62 companies that reported their annual results between April and June, found that they posted revenues of £360.4 billion compared to £346.4 bn in the previous year.
On a like-for-like basis, however, after index changes were taken into account, revenues inched ahead 1%, the weakest increase since mid-2010, according to the online share dealing operator.
Helal Miah, research investment analyst at the Share Centre, said: "If sales are vanity and profits sanity, then UK plc is neither vain nor sane at present.
"The Profit Watch UK shows just how tough conditions have been for UK plc over the past year."
The 62 companies posted £16.6bn in profits, £8.5bn lower than the £25.1bn reported in the same period last year.
Much of the fall can be attributed to telecoms giant Vodafone and the UK's largest supermarket chain Tesco. Vodafone wrote down almost £6bn from its operations in economically troubled countries in southern Europe, while Tesco took £2.3bn of writedowns in the UK and United States.
Discounting Vodafone and Tesco, UK net profits would have risen 2.9% to £25.8bn the Share Centre said, due in large part to the reversal of previous large losses at private equity house 3i.
Much of the weakness was due to continued trouble on the high street as big retailers made up almost two fifths of revenues from companies reporting their annual results in the quarter.
Companies tend to report their results at a similar time to industry peers, making it easier for analysts and investors to compare their performance.
Food retailers grew sales by a modest 1.7% to £110bn, according to the Share Centre data, but general retailers saw a 0.4% fall. They have been hit by the squeeze on shoppers' disposable incomes.
Among the large industries utilities were the weakest, with revenues down 5.6%, dragged down by Perth-based energy giant SSE.
However, the sector also posted a big rise in gross profit, up 8.7%, again driven by the owner of Scottish Hydro-Electric.
Across the market, 12 sectors increased their revenues in the year to the end of March 2013 while ten saw them decline.
Post-tax profit fell in 15 sectors and rose in eight as many companies struggled to pass on cost increases. Overall, companies returned a net profit margin on their sales of 4.6%, down from 7.2% a year ago.
Mr Miah said: "The latest cohort of companies reporting has found it just as difficult as those in the previous few quarters.
"It's true that some big one-offs have made profits seem worse than the broad spread of results would show, but even at the top line, sales growth of 1%, well behind inflation, is meagre at best, and margins have been under pressure across the board."
Among the FTSE-100 which features the country's largest listed companies, 23 reported in the period and collectively saw revenues fall 0.7% to £286.5bn, as the telecoms and utilities sectors experienced weakness.
Net profit fell 37.3% to £14.7bn, hit by Vodafone's and Tesco's woes. Without their impact, net profit would have risen 1.9%.
Some 39 of the 250 also posted results and saw revenue rise 28.6% year-on-year to £73.9bn. Stripping out index changes and a strong performance from oil company Essar Energy, revenues would have dropped 3.4%.
Net profits from the FTSE-250 rose 16% to £1.9bn.