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1 June 2015 Last updated at 22:46 BST
Notorious crime boss, Reggie Kray, penned the 215 exchanges to Carol Clerk, the ghost writer of his autobiography, while serving a life sentence in prison.
Victoria Irvine, a valuer at McTear's Auctioneers, told BBC Scotland the letters were "fascinating pieces of crime memorabilia".
A collection of letters described as being "historically important", which were written by one of the UK's most notorious gangsters, are to go under the hammer in Glasgow.