Hockney fans are in for a real treat.

The first new works in four years from Bradford-born artist David Hockney are to go on show next month.

The artist has produced a new collection of portraits and landscapes - his first since 1998 - which will be exhibited at the National Portrait Gallery and Annely Juda Fine Art gallery in London.

He has used watercolours for the first time, a medium which he had previously dismissed as "wishy-washy".

Five double portraits will be exhibited at the National Portrait Gallery from January.

The centrepiece will be a portrait of Glyndebourne opera chairman Sir George Christie and his wife Mary, which was commissioned by the gallery.

Mr Hockney has been friends with the couple since the 1970s, when he produced the stage designs for Glyndebourne productions of The Rake's Progress and The Magic Flute - currently on display at Salts Mill in Saltaire.

A spokesman for the National Portrait Gallery said: "This acquisition is a significant addition to the Gallery's collection of works by one of Britain's most celebrated contemporary artists."

This commission was the catalyst for a series of double portraits of Mr Hockney's friends, four of which will be displayed alongside the one of Sir George and Lady Christie.

The spokesman said Hockney had been interested in the dynamics of the double portrait for many years.

"In search of a contemporary approach, Hockney began exploring watercolour further earlier this year and found its immediacy and fluidity lent itself to producing portraits directly from life.

"Painted on a large-scale on four watercolour tablets, each portrait was produced in one seven-hour sitting."

Other portraits will also be shown in the Painting on Paper exhibition at Annely Juda Fine Art.

Nine large landscapes inspired by Mr Hockney's visits to Norway and Iceland will be the centrepiece of the show.

Earlier this year, Los Angeles-based Mr Hockney travelled to the countries for the longer daylight hours. The landscapes he produced are in bold colours and have been painted on multiple sheets of paper.

The artist had been inspired to use watercolours after seeing work by 19th century painter Thomas Girtin at Tate Britain.

Painting on Paper also includes nine large double-portraits, three single portraits and studies of bonsai trees.

Mr Hockney was born in Bradford in 1937 and graduated from the Bradford School of Art in 1957.

He then studied at the Royal College of Art between 1959 and 1962.

l Five Double Portraits runs at the National Portrait Gallery from January 16 until June 29 and admission is free.

David Hockney: Painting on Paper is at Annely Juda Fine Art, Dering Street, London, from January 17 until March 1.