A LETTER from Scots economist Adam Smith to a British diplomat about trade deals with "revolted colonies" is to go on sale for £75,000.

The Kirkcaldy-born thinker was a leading figure in the Scottish Enlightenment and laid the plans for the free market economy in his 1776 work The Wealth of Nations.

Now a two and a half page letter on customs, smuggling and overseas deals with the newly independent United States of America will be on offer for a five-figure sum at the Edinburgh Book Fair.

Penned in 1783, the piece will be displayed by London-based dealer Peter Harrington and was composed while Smith served as Commissioner of Customs for Scotland.

It was written to statesman William Eden three months after the UK formally recognised the secession of its 13 American colonies as Eden pondered how to make up for the lost trade.

Smith tells Eden he will answer all questions "concerning our future commercial connexions with our thirteen revolted colonies" and ends with a request for all future post to be addressed to his official title.

Smith states: "I once had the vanity to flatter myself that I was the only Adam Smith in the world; but to my unspeakable mortification, there are two or three others of the same name in this town, and my letters are sometimes gone wrong."

A book from Smith's library will also be on sale, as will a rare copy of The Journal of a Tour of the Hebrides by Samuel Johnson and James Boswell and a Robert Louis Stevenson first edition.

The March 24-25 fair at the Radisson Blu Hotel is free to enter.

Dealer Pom Harrington said: "This is Scotland’s leading antiquarian book fair and we are bringing with us a selection of books which should particularly appeal to Scottish book lovers. Edinburgh is an important literary centre which has inspired hundreds of writers and we look forward to meeting visitors to the Book Fair who love rare books as much as we do.”