Unveiling the 'greatest collection of 20th Century British Art ever to auction'

This week sees the start of what has been called the 'greatest' auction of 20^th century British art ever.

The three-part sale begins this Wednesday, June 15, at Sotheby's in London and features works by some of the most famous artists the country has ever seen, including Lucian Freud, Henry Moore, Patrick Heron and Stanley Spencer.

The pieces were collected by Wilfred Evill between 1925 and 1960. They have been largely kept out of the public eye since a memorial exhibition for the late Evill at Brighton City Art Gallery in 1965.

Also included in the sale, which is expected to make in excess of £12m ($19.5m) overall, are pieces of rare sculptures, furniture and porcelain.

Stanley Spencer's lively work will be the auction's main attraction

Stanley Spencer's stunning 1935 painting, called Workmen In The House, has been earmarked as the top lot, with a guide value of between £1.5m-2.5m ($2.4m-4m). It is one of his best known works, yet is one which has been seen very little in public.

Evill clearly rated it highly as he paid £250 for it in 1937. The auction contains the largest group of Spencer's painting ever to go on sale together, making it hugely significant. It is therefore not surprising that other works of his, like The Village Lovers and Sunflower and Dog Worship, are also estimated to sell for at least £1.5m ($2.4m).

Top lots by other artists include Lucian Freud's minimalist chalk, pen and ink piece entitled Beach Scene with a Boat, which could reach a price of £600,000 ($974,000) and Patrick Heron's exuberant oil painting called The Blue Table with Window.

Vivid colours dominate Heron's 'abstract' work

The work, which Heron himself said was 'terribly abstract', is estimated to sell for between £250,000-350,000 ($405,000-568,000).

The most prominent sculpture included in the auction is Henry Moore's bronze Rocking Chair No.3. The intimate object, depicting the bond between a mother and her child which became one his main themes, has also been given a high estimate of £1.2m ($1.94m).