LONDON (Reuters) - Britain is to regulate electronic cigarettes as non-prescription medicine from 2016 in an attempt to improve quality, though the country's drugs watchdog said they would still be sold in convenience stores.

Healthcare authorities around the world are grappling with how to deal with the battery-driven devices, which allow users to inhale nicotine-laced vapor and are increasingly popular as a less harmful alternative to smoking.

A few countries have banned them - such as Brazil, Norway and Singapore - while others are opting for varying degrees of regulation, in some cases including restrictions on advertising and curbs on their use in public places.

Under the new British system, manufacturers will have to prove the quality of their products and demonstrate that they deliver the correct amount of nicotine. But they will not need to conduct clinical trials.

The Medicines and Healthcare products Regulatory Agency (MHRA) said on Wednesday that existing e-cigarettes on the market were not good enough. However, manufacturers have time to raise their game and apply for a license, allowing them to sell regulated devices as over-the-counter products from 2016.

A growing number of established tobacco companies are investing in the e-cigarette market worldwide, including Lorillard, British American Tobacco, Imperial Tobacco, Reynolds American and Altria.

(Reporting by Ben Hirschler; Editing by David Goodman)

[A man uses an E-cigarette, an electronic substitute in the form of a rod, slightly longer than a normal cigarette, in this illustration picture taken in Paris, March 5, 2013. REUTERS/Christian Hartmann]