Taro Aso, Japan's prime minister, has announced plans for an August 30 general election that opinion polls suggest could mark the end of the divided and dispirited Liberal Democratic party's long dominance over the world's second largest economy.

The decision to go to the polls more than a month before legally required appeared intended to secure Mr Aso's position in the face of a revolt by party colleagues who blame him for a disastrous defeat in the Tokyo municipal assembly election on Sunday.

However, it means the LDP, which has ruled alone or in coalition for all but 11 months of the past 53 years, has little obvious way to regain the political initiative in time for a vote that polls and analysts say looks increasingly likely to be won by the decade-old Democratic party of Japan.