Income at the employment and skills charity the Shaw Trust increased from £103m to £132m in the financial year ending 31 March 2017.
But the increase, which is revealed in accounts published at Companies House last week, occurred mainly because of the value of assets acquired from the purchase of three new schools, and cannot be spent.
The Shaw Education Trust, which is sponsored by the Shaw Trust, now owns eight schools, which help disadvantaged pupils.
According to the accounts, underlying economic conditions are "challenging", mainly because of the ending of contracts from the government's welfare-to-work programmes.
"Economic conditions in the main UK market continue to be challenging, with a further reduction in clients referred to the main welfare-to-work programme, which has resulted in an overall fall in incoming resources from charitable activities," the accounts say.
"Referrals to the Work Programme ended in March, but the trust secured extensions to its Work Choice contracts until September 2017. It also secured a one-year contract with the Scottish government to deliver its Work First Scotland employability programme."
The accounts describe the ending of Work Choice and the Work Programme as the trust's "main risk".
It is attempting to diversify income in response to this and, in June, acquired the employment and skills not-for-profit Ixion Holdings from Anglia Ruskin University. The Scottish social enterprise Forth Sector became a subsidiary of the trust in January.
The accounts reveal that the number of staff at the Wiltshire-based trust increased from 1,597 to 1,814 and the number of employees earning more than £60,000 increased from 46 to 56. The document says this "is substantially due to the conversion of three new schools into Shaw Education Trust during 2016-17".
The highest salary paid during the year was in the £170,000 to £180,000 pay band. The recipient of this money is not identified in the accounts.
The trust's investments portfolio, which fell in value by £0.7m in the previous year, grew by £2.7m.