Revenues on an actual basis fell 3.7 per cent from £6.89bn to £6.86bn in 2015, while profit before interest, tax and amortisation (PBITA) fell 1.5 per cent from £397m to £391m.
Statutory earnings plummeted 94 per cent to £8m, while earnings per share went from 9.4p to 0.5p, a drop of 94.6 per cent.
G4S said this came "after charging onerous contract provisions of £65m, restructuring of £44m, losses on businesses being sold or closed of £40m and non-cash charges of £106m relating to the amortisation/impairment of goodwill".
Net debt also soared to £1.78bn, up from £1.64bn last year, meaning it now has a 3.3 times debt to earnings ratio. The business said it planned to cut this to 2.5 or lower in the next 12 to 24 months.
On a constant basis, the group managed a slight increase in both revenues, up 3.9 per cent to £6.4bn, and profits, up 5.6 per cent to £427m.
The board is recommending a final dividend of 5.82p per share, in line with last year, taking the full year dividend to 9.41p per share - up 1.8 per cent.
But investors were unimpressed by today's news: G4S' share price was down more than five per cent on the open and continued tumbling during early trading, dropping as low as 12.5 per cent.
Why it's interesting
The scandal-prone business is never out of the headlines, most recently being criticised for having put asylum seekers in houses with red front doors, leaving individuals at risk of physical abuse.
And there appear to be few benefits to delivering the Home Office's contracts on this front, for which G4S provides accommodation, transport and subsistence services while asylum seekers' claims are being processed.
G4S bemoaned its "onerous legacy contracts" being run in the UK, the main reason for today's poor figures.
"We experienced a significant increase in the number of new asylum seekers between November 2015 and January 2016 and as a result the number of asylum seekers in our care increased by 9.6 per cent year-on-year... As a result of a material increase in the number of asylum seekers we received between November 2015 and January 2016, we have increased the Compass onerous contract provision by £20m to £31m," the group said.
If the contract is extended by the government until August 2019 it would be even worse for G4S, resulting in a further provision of £57m.
What G4S said
Chief executive Ashley Almanza said; "During 2015 we made substantial progress with the strategic and operational transformation of G4S. Our portfolio management programme combined with our investment in sales, innovation and re-structuring is reflected in the results of our continuing operations where the group's revenues rose by four per cent and underlying earnings rose by 14 per cent. These programmes remain a priority and are expected to sustain our growth and strengthen our balance sheet.
"We continue to actively manage our onerous legacy contracts in the UK which were entered into prior to 2013. We have had to increase the provisions in relation to these contracts. We have also established robust controls governing new major contracts.
"Against a background of global economic uncertainty, demand for our services has remained resilient and growth accelerated in the second half of 2015, providing good support for further operating and financial progress in 2016."
G4S' turnaround has been weighed down by the impact of a surge in asylum seekers since last November.