In May, two bottles of whisky sold via a British online auction site for £12,050 ($20,800). The labels were missing and the contents were described as unfit for human consumption, but the reason for their value was that these were from the SS Politician, a ship wrecked off the Scottish island of Eriskay in 1941.

Photo gallery: Make Dad's day with top notch Scotch

This real-life event was the inspiration for the 1947 Compton Mackenzie novel Whisky Galore, filmed in 1949 as Whisky Galore! In 1987, eight bottles were retrieved from the wreck and sold for a total of £4000. In 2010, another Whisky Galore bottle sold for £4200.

This is an indication that old and rare whisky, even bottles that can't be drunk, is now regarded as an investment. Well, some of it. The Times estimates that if you had invested in the top 100 performing whiskies in 2008 you would now be sitting on a profit of 306 per cent, ''far better than the returns from any major stock market''.

Which explains why the secondary market for rare whisky in Britain is rapidly expanding. According to The Times, just over 2000 bottles were sold at auction in 2008. This rose to more than 14,000 bottles in 2012, with no sign of slowing.