Twenty years ago today, glasses were raised throughout Ireland and across the world in honour of St. Patrick's Day. But HM Customs had a special reason to celebrate, because one of their least favourite scams was to be made illegal at midnight - and it was something green. In this case, green diesel. Now, we're not talking about environmentally friendly diesel here. This is diesel intended to be used for off-road vehicles, such as agricultural machinery. And there's a specific place for it to be used: on the Irish side of the border shared between the Republic and the United Kingdom, the only land border that either nation has to worry about. Diesel for agricultural use is a lot cheaper than normal 'white' diesel for road vehicles, because it's subject to a much lower rate of fuel duty. So in order to stop people cheating the taxman from his rightful share, it's marked with dye - green in Ireland, red in Northern Ireland - and the police conduct random checks to make sure that only properly taxed fuel is used.
By the 90's, diesel engined cars were becoming more and more common, so the practice of selling red or green diesel to normal road users at half the price of normal diesel became a scam that criminals could take easy advantage of. The police occasionally stopped vehicles to check them, but there was one trick they couldn't prevent. It was illegal to buy red or green diesel in each respective country, and it was illegal to transport the fuel across the border - but it wasn't actually illegal to buy green diesel if you happened to be in Northern Ireland.
So the enterprising criminals of the border (of which there were many), would drive a tanker up to a point a few metres inside Ireland, run a pipe across the border, connect it up to a pump in the UK, and start selling.
The police forces on both sides of the border did their best to prevent this trade in all the traditional ways, like actually going up to the criminals and arresting them. But the borders were a lawless place, and it was impossible to keep every mile constantly under surveillance. Special operations were launched to try, but as soon as they put one group of smugglers out of business, another would spring up overnight.
So they did the next best thing: they changed the law. From midnight tonight (twenty years ago, that is), green diesel became just as illegal in Northern Ireland as red diesel, and the police could seize the vehicle for the crown if they found the Irish fuel in the tank.
And did this solve the problem of fuel fraud in Northern Ireland? No. Don't be silly. The criminals just found new ways to make money - for example, by passing the fuel through cat litter to filter out the dye. Plus there are all kinds of other cross-border fraud possibilities, such as tobacco smuggling. To this day, both the PSNI and the Garda Síochána are still struggling to keep up with the ingenuity of the criminal gangs that live on the border.