Courts should be "very slow" to overturn wills left to charity because disappointed relatives are unhappy with their contents, according to the Court of Appeal's judgement in a recent case involving the RSPCA.
But the court upheld a High Court ruling that deprived the charity of a £2m legacy on the grounds that the facts of the case were "quite exceptional".
Lord Neuberger, the Master of the Rolls, gave the reasons this week for the court's recent decision to reject the RSPCA's appeal over the legacy.
The charity had challenged a High Court ruling overturning a will that left the charity a 287-acre farm in North Yorkshire.
Christine Gill, the daughter of the deceased, won a long court battle against the charity in October, after arguing that her father had coerced her mother into leaving everything in the will to the charity before he died in 1999.
The Court of Appeal decided that Gill's mother suffered from a rare mental condition and did not "know or approve" of the will's contents.
Lord Neuberger said courts should be very slow to find that a will does not represent the wishes of its owner because its contents are surprising or unfair.
"There may be a danger of this submission being seen as something of a green light to disappointed beneficiaries, and in particular to close relatives of a testatrix who have not benefited from her will, to challenge the will even where it has been read over to the testatrix, or to appeal a full and careful first instance decision upholding a will's validity," he said.
"It is therefore right to emphasise that the facts of this case are quite exceptional."
Mark Watts, chief executive at the RSPCA, said the charity remained concerned that the case may have eroded the freedom of people to leave their money to whomever they choose.
"Charities as a whole are facing more challenges in relation to disappointed relatives disputing their wills," he said. "This is having serious implications for the charity sector and comes at a time when charities are feeling the financial fallout from the credit crunch and when more is being asked of them."
Mark Keenan, a partner at the law firm Mishcon de Reya, which represented Gill, said charities should not be alarmed by the decision.
"The Charity Commission provides useful guidance as to how charities should approach this type of case," he added. "As the trial judge said, 'charities are like any other commercial litigants'. They are not obliged and should not feel compelled to defend or to take to trial cases such as this."