One day, the National Crime Agency received information that a tugboat

sailing off the coast of Scotland might be carrying drugs.

They sent out a low - flying plane to find it.

Then, a Royal Navy warship and a large Border Force ship to intercept it.

Below deck, hidden in a tank, they found 3. 2 tonnes of cocaine, worth 512 million pounds.

It was the biggest ever seizure of Class A drugs in UK history.

Good news for the government, you might think.

But in terms of how we measure the economy, this was actually bad news.

Sales of illegal drugs like cocaine are counted towards our GDP, or Gross Domestic Product,

the main way the government measures how well the economy is doing.

So that tugboat getting intercepted meant lower GDP.

But governments want GDP to go up - what they call " economic growth ".

To calculate GDP, we count everything that 's made in the UK, minus what we put into making it.

So, if a coffee shop sells 100 pounds worth of cups of coffee,

but spent 10 pounds on buying the coffee beans to make it,

their contribution to GDP would be 90 pounds.