As a boy growing up in Sikkim, the Indian state nestled below the Himalayas, Rajendra Gurung remembers how, before leaving the house to go shopping, his parents would always ask each other: “Have you got the bag?”

Back then, no shopkeeper used plastic bags. Families took their own, made of cloth. Meat, fish and cheese came wrapped in a banana leaf, tied with bamboo twine. If people bought cooking oil, they took an empty bottle or can.

But in the early 1980s, plastic bags started to become the norm. “The first ones were actually prized possessions because they were re-usable,” says Gurung. By the mid-80s, they were used for everything.

Yet discarded plastic bags blocked drains, and even caused a spate of landslides. In 1998, Sikkim banned their use.

Now, at the vegetable market in Lal Bazar in the Sikkim capital, Gangtok, most people come armed with cloth bags – and those who have forgotten them can buy one from the lines strung up at vegetable stalls. A street vendor selling fermented soya bean wraps his produce inside a leaf from a fig tree. Even bulky items like metal pails are covered with newspaper.

A 2014 survey by Toxic Links, a New Delhi organisation, found that in Gangtok and other main towns, plastic bags are now rarely used.

Sikkim’s progress is being studied closely by other states. These include Mumbai, the commercial capital, where drains clogged by bags have caused flooding in the streets during monsoon season.

A combination of factors made the ban successful, says Gurung, who now heads the Ecotourism and Conservation Society of Sikkim. “Shopkeepers were not given licences, and licences weren’t renewed every year if they were using plastic bags. Inspectors watched them. Heavy fines were imposed. CCTV cameras were installed. Consumers were also made aware,” he says. Campaigns in schools educated children on the damage plastic can do.

A trader uses a leaf to pack produce in Sikkim. Photograph: Amrit Dhillon/The Guardian

Out of India’ s 29 states, 25 have some kind of plastic ban. But it is rarely enforced by the authorities and ignored by residents. Part of Sikkim’s success is down to people’s respect for the law. Gurung attributes this partly to the fact that until 1975, the state was a monarchy. People obeyed the king instinctively and this same attitude was transferred to the chief ministers who succeeded him.

The state also has a large Buddhist minority, which means respect for nature is widespread. “Every forest is a sacred forest, every lake is a sacred lake, the Himalayas are sacred. This reverence for nature – combined with our disciplined habits – feeds into the desire to protect the environment,” says Prem Das Rai, the MP for Sikkim.

However, not all is perfect. Some people have begun using non-woven polypropylene bags. They look and feel like fabric but they are in fact made of plastic and are equally damaging to the environment. Gurung says consumers need to be educated about this before they start becoming popular.

In 2016, Sikkim took its plastic ban further, by ending the use of bottled water in government offices and functions. Ministers have started taking reusable water bottles to the office and filtered water is served in jugs or glasses.

On top of this, tourists are being told not to bring in plastic bottles of water. To encourage them, clean water points have been set up where water, certified as safe by the government, is sold to fill reusable bottles.

Gurung believes the best way to stop tourists bringing in, or asking for, bottled water is for restaurants and hotels to display certificates proving that the water in their kitchens has been purified.

Sikkim has also banned the sale and use of styrofoam and thermocol disposable plates, cutlery and food containers. “We are going to have to go back either to washing dishes, as before, or using plates made of leaves, areca nut and sugar-cane bagasse, and spoons and straws made of bamboo,” says Priya Shrestha, team leader at the World Wildlife Fund in Gangtok.

Sikkim’s success will not be easy to replicate in other states. Buying vegetables and food put in plastic bags is an ingrained habit. They are convenient, hygienic, light, durable and cheap. Surveys have shown that 99% of vegetable sellers in most cities use plastic bags.

Sikkim is also small. Its population is only 610,000 people. This is compared with Maharashtra, of which Mumbai is the capital, which has just imposed a stringent ban on plastic bags out of concern for the flooding caused by mountains of the stuff. Its population is more than 100 million.

Nonetheless, Sikkim’s relentless campaign to educate the public is one feature that can be replicated in other states, says Gurung.

“With large populations, random fines alone cannot work. You have to have intensive campaigns like ours to change people’s habits. Only when the message is lodged in the mind does a ban work and for that, you have to start, as we did, in schools.”