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For the uninitiated, entering a public lavatory in China can be a horrifying experience.

In smaller cities, or the countryside, the sight of an open trench filled with excrement, coupled with a suffocating stench of sulphur and ammonia, is often enough to send even the bravest tourist whimpering back to their hotel.

In the 1990s, a third of all complaints to tourism officials in Beijing concerned the design, and odour, of public lavatories.

China has battled stinky loos for at least 2,000 years. In the Kingdom of Wei (220-265AD), visitors to the palace bathrooms would find boxes of dates to stuff up their noses and ward off unpleasant odours.

However, both flushing lavatories and toilet paper were invented in China, although only initially for the use of the emperor.

Today, however, Chinese scientists have claimed victory in their battle to improve public rest rooms, unveiling a bacterial spray that can, they say, almost eliminate the smell of putrefaction.

First, a set of six strains of bacteria work to break down the odorous compounds and then a perfume made from orange peel lightly scents the air.

The "smell-free lavatory" study from the Chinese Academy of Science was declared the "ultimate" cure to an "urgent" national issue.

"Five scientists have worked on this from 2011 to the beginning of this year," said Dr Yan Zhiying, a bacteriologist with the academy's Chengdu Institute of Biology, adding that they had spent ￡140,000 on the project.

"Some local government officials here visited a sewage plant and saw that the treatment technology had come from Japan. They wanted a home-grown solution so they asked us to work on it," he added.

"We extracted bacteria from all type of excrement, human, pig, chicken and duck, and we tested our compounds one by one," he said.

"The smells coming out of public lavatories, or cesspits, or rubbish tips, are made up of more than 160 different compounds," he explained, adding that their bacteria, including a strain from the lactobacillus, saccharomycetes and actinomycetes families, can convert and absorb many of them.

He boasted that the Chinese formula, which costs around ￡5 per litre, has no side effects and can be used to fend off the stench of any type of biological decomposition.

More recently, Beijing has waged a war to improve conditions in public lavatories, first introducing a star-rating and then, two years ago, drafting a rule that no more than two flies should be present in any of the city's facilities at the same time.