BANGKOK, Sept 20 (Reuters) - Thailand's legislators will renew a push for an overarching law on use of cannabis for medical and research purposes, a senior lawmaker said on Wednesday, more than a year after the narcotic was legalised without proper regulations.

Last year, Thailand became the first country in Southeast Asia to decriminalise cannabis, but in the absence of specific measures, the government had to hastily issue rules to prevent its unchecked use, particularly among children.

The new law will target an industry projected to be worth up to $1.2 billion over the next few years, with cannabis shops having sprung up across the capital Bangkok and tourist hot spots, such as the resort island of Phuket.

"Cannabis will be - double underline - for medical purposes and research," said Saritpong Kiewkong of the Bhumjaithai party, which spearheaded the decriminalisation and is now the second largest component of Thailand's 11-party coalition government.

"There is no policy for recreational use," the lawmaker told reporters in parliament, adding that such measures were not yet being considered.

The draft law, which consolidates measures against public use that the government now relies on to rein in misbehaviour, is expected to take a year to finalise and pass.

It covers permits for growing plants, sales and distribution, and tighter measures against sales in temples, schools and amusement parks.

Last week, Prime Minister Srettha Thavisin said he supported only medical, and not recreational, use of cannabis.