More than 120 kilograms of cocaine were seized by police in Scotland last year after being smuggled across the border.

It is the most popular hard drug in Scotland and Scots take more of it individually than anyone else in the world.

But how does cocaine - which is produced nearly 5000 miles away in the jungles of South America - get to Scotland?

Cocaine is made from the leaves of the coca plant, which is grown in Colombia, Bolivia and Peru by farmers under the control of drug syndicates.

Despite a years-long war on the trade by the authorities Colombia remains the world's largest producer of cocaine. It exported around 900 tonnes of the drug in 2016.

It takes around a tonne of coca leaves - worth 90p to farmers - to produce a kilogram of pure cocaine. A single gram sells for about £70 in Scotland.

The leaves are hand-picked, dried and shipped to labs run by the drug syndicates, where they are processed into a paste which is dissolved to turn it into the powdered form of cocaine.

It is then packed into trucks or cars and trafficked to the coast, where it is loaded on to boats. A small amount of coke is also trafficked out of South America by air.

Some traffickers even use commercial cargo ships to smuggle cocaine in bulk, hidden among the tens of thousands of containers which pass through European ports each day. Traffickers intimidate locals and bribe officials on both ends of the route to hide their activities.

Most of the cocaine which arrives in the UK each year - around 30 tonnes of it - enters Europe via Spain or Portugal, often after stopping off in the Caribbean or West Africa.

The largest haul ever seized in the UK - three tonnes of high-purity cocaine worth more than £500m - was found aboard a trawler off the east coast of Scotland in 2015.

Its crew is believed to have picked it up in South America and stopped off in Tenerife before heading for Britain. Packets of cocaine have even washed up on beaches in northern Scotland.

After being trafficked through Europe, cocaine is transported to major cities like London, Liverpool and Manchester, where it is cut, packaged and distributed by dealers.

Detective inspector Allan Elderbrant, from Police Scotland's substance harm prevention unit, said: "Gangs have their own distribution links, their own supply routes.

"They'll come into major cities - a lot of it will come into the north of England - and then across the border into Scotland from there."

"There are some Scottish serious organised crime groups who are heavily involved in the distribution of controlled drugs," he said.

"But there are organised gangs in Liverpool and Manchester, if they can get the links to a Scottish gang that will make it easier for them. It also minimises conflict here in Scotland.

"There will be groups operating from the likes of Liverpool, for example, that will use their own gang members to bring it into Scotland."

The quality of British cocaine has risen in recent years as an unintended consequence of a crackdown on the substances used to cut it.

"A few years ago purities across the UK were incredibly low because of the ready availability of benzocaine as an adulterant," said Allen Morgan, an expert who advises on legal cases involving drugs.

"They clamped down on the raft of online benzocaine suppliers and as a consequence the cocaine market evolved into the high purity model that we are seeing today."

However, Scottish coke tends to be less pure because we are further down the distribution chain.

Katy MacLeod, from the Scottish Drugs Forum, said: "We get much higher purity in London and you tend to find the further north it goes the more adulterated it becomes. It will often be cut each time it's passed down the chain."

According to the 2018 edition of the Global Drug Survey, Scots take more cocaine per session than anyone else in the world.

We use about 1.2g in an average session, compared to a global average of around 0.5g. The low quality of Scottish cocaine is one potential explanation.