Composition With Circles is Riley's latest major piece

Composition With Circles, an 18-yard wide wall drawing, is part of an exhibition opening at Tate Britain in London on Thursday.

The gallery has also bought another work, Evo� 3, which Riley created this year.

Riley's works evoke the pop art era of the 1960s

Riley's vibrant abstract paintings from the 1960s, using simple black and white and later colour, are among the best-known of the era.

She is noted for her visually challenging works which often play tricks on the eye, generating sensations of movement, light and space.

Riley, who is now 72, was inspired by her childhood in Cornwall, and the impact of the Cornish landscape's light and colour.

Describing her art, she once said: "The eye can travel over the surface in a way parallel to the way it moves over nature.

"It should feel caressed and soothed, experience frictions and ruptures, glide and drift."

The Riley retrospective runs at Tate Britain from 26 June to 28 September.