David Cameron says it is "right" that the Tories and Liberal Democrats give up a £520,000 bequest from a former nurse amid confusion over whether she actually meant the money to go to the Government.
The Prime Minister said the wording of Joan Edwards' will made clear that her intention was for the money to "benefit the nation" rather than political parties.
The legacy sparked a bizarre row after a copy of the document emerged.
Conservative and Lib Dem officials previously briefed that they had split the money because it was earmarked for "whichever party was in government".
But the text obtained by the Daily Mail showed Miss Edwards – who died in September aged 90 – identified the beneficiary as "whichever government is in office at the date of my death".
As the backlash gathered pace, both coalition partners declared they would hand the funds to the Treasury as a gesture of good faith.
However, shortly afterwards the executors of Miss Edwards' will, Bristol solicitors Davis Wood, released a statement insisting that she had indeed intended the cash to go to political parties.
"The will was drafted by a solicitor at Davis Wood in 2001," the law firm said. "At the time, the solicitor specifically checked with Miss Edwards about the unusual nature of her proposed bequest and it was confirmed by Miss Edwards at the time of her instruction that her estate was to be left to whichever political party formed the government at the date of her death."