Scotch whisky bosses have agreed to break with tradition and change the rules on production of the spirit in a controversial move that has angered some purists

For centuries, the whisky has been traditionally aged in barrels previously used to mature spirits such as cognac, brandy or sherry, giving the drink its unique taste.

However, the Scotch Whisky Association (SWA), which enforces how Scotch is made and marketed, has now relaxed the rules to allow barrels previously used for other spirits, such as tequila, to be used - so long as it does not taste more like the Mexican spirit than the Scottish one.

Karen Betts, the SWA's chief executive, said: "This change is consistent with Scotch whisky's heritage and traditions, and strengthens our foundations into the future."

To count as Scotch whisky, the spirit must be distilled in Scotland from water and malted barley and aged in the country for three years in oak casks.

Distillers claim that the change allowing different types of barrels will allow them to broaden their product range and appeal to a younger market.

However, Gavin Hewitt, former chief executive of the SWA, told the Wall Street Journal: "Scotch needs to be judged by its colour, taste and tradition. Clearly if you then had a whisky that tasted of tequila, if it used an extequila cask, it would not be Scotch."