Blake's paintings aimed to illustrate The Grave but they were never used

The paintings, made in 1805 to illustrate a Robert Blair poem entitled The Grave, were rediscovered in 2001.

Sotheby's expect the paintings to fetch a total of up to $17.5m (�10m) when sold individually at auction on 2 May.

Last year the government placed a temporary export ban on the paintings but UK galleries and collectors failed to meet the �8.8m asking price.

Sale 'an affront'

The English artist's watercolours were commissioned to illustrate an edition of Blair's 18th Century poem, but were ultimately not used in the volume.

They were lost in 1836 but were unearthed in a bookshop in Scotland in 2001. They are being sold by an anonymous investment fund.

The prospective sale has disappointed admirers of the late artist, who had hoped the 19 paintings would remain as a complete set in the UK.

"When you split these things up it is an affront to everyone who loves Blake," Blake Society chairman Tim Heath told The Daily Telegraph.