THE trade in rare whisky is big business – and so is counterfeiting.

The most sought-after bottles sell at auction to wealthy collectors for more than £1 million a pop.

Sales rooms seek to ensure no knock-off items are offered to their clients, but the trade in counterfeit drinks costs the UK economy more than £200m in lost revenue each year, according to a 2018 European Union study.

Now St Andrews University scientists say they've worked out a way to tell a dram fine bottle from a fake – without ever removing the cap.

The technique involves using lasers to measure what's inside the glass.

It was developed by experts from the Fife institution's School of Physics and Astronomy using laser spectroscopy. This uses beams to scatter the light into different colours, the precise colours of which identify materials ranging from bacteria, food and drink, through to the paint on sculptures and explosive powders.

A previous attempt with whisky was hampered by the fact that the glass bottle can create an even bigger signal than its contents, and so a small quantity of the amber nectar had to be removed for testing.

The new method uses a glass element to shape the light and produce a ring of laser light on the bottle surface and a tightly focussed spot within the liquid contents.

As the signal from the bottle and the signal from the liquid are at different positions, a detector can be placed to record only the signal from the liquid, meaning the bottle contents can be assessed while the seal stays tight.

Professor Kishan Dholakia said: “Personally, I hate it when I have to spare a drop of whisky for validation checks. I’d much rather drink the whole bottle.

"Laser spectroscopy is a powerful tool for characterising the chemical make-up of many materials, but to use it to characterise alcohol in its original container in this simple way is really exciting."

It's thought that the method – which has also be proved on vodka and gin – will soon enter widespread use.

The research is has been published in the journal Analytical Methods.