For all the talk of global currency wars in recent weeks, central banks have had little success in reining in their rising currencies against the sliding dollar.

The overriding theme in currency markets remains one of dollar weakness as investors await an expected extension of the Federal Reserve’s quantitative easing programme at its policy meeting next month.

The dollar’s lurch lower – it has dropped more than 6 per cent on a trade-weighted basis since the start of September – has prompted central banks of emerging markets across Asia to intervene more aggressively to stem gains in their currencies to protect exporters. Between September 27 and October 11, central banks in South Korea, Malaysia, Indonesia, Thailand and Taiwan collectively purchased $28.74bn, according to estimates by IFR Markets.