The U.K. government will go to the country's highest court Tuesday in a bid to force open a £475 million ($640 million) charity fund set up 90 years ago with the intention of paying off the national debt.

The "National Fund" was opened in 1928 by an anonymous benefactor who donated £500,000, but on the condition that it must remain untouched until the U.K. raises enough money to pay off its entire national debt.

While the fund currently stands at £475 million, it represents just 0.06 percent of the U.K's estimated £1.7 trillion debt.

Attorney General Jeremy Wright will urge High Court judges on Tuesday to change the terms of the trust fund and release the money to pay off some of the U.K.'s debt.

"Almost 90 years ago, an anonymous donor bequeathed money to the nation and yet we have not been able to put it to good use," Wright said. "We have been working with the Treasury, trustees and the Charity Commission to find a solution consistent with the donor's original objectives of extinguishing the national debt."

Barclays, which oversees the management of the fund, has for years tried to obtain permission to gain access to the money, to make it available for charitable grants or hand it over to the Treasury.