LONDON - THE Tate Britain museum bought a rare sketch by Peter Paul Rubens with help from several art and heritage foundations to keep it from being sold abroad, the museum said on Thursday.

The Tate paid 5.7 million pounds (S$14.59 million) for the sketched version of his larger painting, The Apotheosis of James I - which depicts King James I being carried to heaven.

The completed artwork was painted onto the ceiling of Banqueting House at Whitehall, the 17th century London residence of the monarch.

The sketch had been in the family of late Anthony David Brand for two centuries.

When he died in January, the family offered the museum the chance to buy the sketch at a discount for tax purposes.

The museum launched a fundraiser with the help of other organisations, including The Art Fund and the National Heritage Memorial Fund, to buy the work before it could be released on the open market and potentially sold overseas.

'The Banqueting House ceiling is the most important painting set within an architectural context in England, and this sketch is the key to its composition,' said Mr David Starkey, a former history professor at the London School of Economics who now works as a broadcaster and writer.

'The loss of the sketch would have been a fundamental betrayal of our national heritage.'

Rubens created the study for King Charles I in the 1620s as a preview of his Whitehall commission. The Banqueting House survived the fire that burned down the rest of the palace in 1698.

The sketch for The Apotheosis of James I has been on exhibition at the museum since late March. -- AP