A series of Mahatma Gandhi's letters and photos will be auctioned at Sotheby's next month.

The documents belonged to Hermann Kallenbach, one of the leader's closest friends - and include personal letters from Gandhi's sons.

Dr Gabriel Heaton, Sotheby's Book and Manuscripts expert, said: the lot contains "very intimate and personal letters covering many decades".

The documents will go under the hammer as a single lot in July, with an estimate of around £700,000.

With blades of bloody grass - supposedly from where Gandhi was assassinated - selling at £10,000 in April - the lot is bound to attract plenty of interest.