The OECD said the UK economy may need more stimulus and a further round of quantitative easing may be necessary.
The OECD said UK growth remained flat, and is only expected to "pick up momentum" towards the end of next year. The Paris-based economic think tank forecasts that the UK economy will grow just 0.9% this year, after shrinking 0.1% in 2012.
Angel Gurría, the OECD's secretary general, said a "particularly bright spot" in the UK was employment figures.
More top news
The figures by the Global Slavery Index are a third higher than previously thought.
Sara Di Pietrantonio, 22, died in Rome on Sunday.
A vote to remain in the EU will see Brussels exert more power over the NHS, according to the Cabinet minister.