The charity said the increase was largely due to a 74 per cent rise in income from institutional donors to £39.6m in the year, which ran until the end of June 2015. The £80.4m income was a record high for the charity, it said.
Of these funds, the charity received £15m from the Department for International Development and others to help with disasters including the Ebola crisis in west Africa and the earthquakes in Nepal.
The charity received a further £10m from DfID during the year for a water, sanitation and hygiene project in south Asia, as part of a five-year scheme worth a total of £25m.
Income from trusts, foundations and major donors also increased by 24 per cent to £8.3m.
"While we do not seek growth in income as an end in itself, we are proud that this increase represents our success in persuading individuals, institutions and corporates of the importance of our mission and of their confidence in our ability to deliver change for girls and boys in the world’s poorest countries," the report says.
Voluntary income fell from £33.3m in 2013/14 to £31.8m last year, the accounts show. This included a small fall in funds for child sponsorship, the largest source of income in this area, from £18.8m in the previous year to £18.5m over the last 12 months. Legacy income also fell from £1.4m to £605,000 in 2014/15.
The charity spent £71.3m over the course of the year, up from £63.5m in the previous year.
The charity increased the number of people it employs by 10 to 188 by the end of the year, including 20 part-time staff.
But the number of hours from volunteers, interns and people on work placements fell from 13,600 in 2013/14 to 8,100 last year.
A spokesman for the charity said the figure, which was an estimate, had also fallen in the previous financial year.
"This is due to a number of factors, including the changing needs of the charity and the fact that a number of volunteers went on to gain paid employment either at Plan or elsewhere, in part due to their experience with us," he said.
Tanya Barron, chief executive of the charity, was the highest-paid individual at the charity on a salary of £110,433, up from £109,339 last year, the accounts say. She also received employer pension contributions of £18,842, compared with £18,656 in 2013/14.