The High Court ruling in the RSPCA disputed legacy case could prompt others to try their luck and contest wills left to charity, fundraisers have warned.
University lecturer Christine Gill will inherit a £2.3m estate originally left to the RSPCA after the High Court agreed that her mother had been coerced into signing the will by her father.
Gill Raikes, director of fundraising at the National Trust, which benefits from about 2,000 legacies a year, said more cases were inevitable after the publicity about the case.
"We are watching this with great concern," she said. "I would think it will make more people want to try their luck. Whatever the details of this particular case, it will make people more aware that they can contest a will. That is quite damaging."
Raikes said the proportion of National Trust legacies that were contested varied widely, but on average about 10 per cent were disputed - equivalent to about 200 a year.
"We feel passionately that when a will is made to the National Trust, it is absolutely our duty to pursue it," she said.
"Contested wills can sometimes be very painful, but we feel very sure that in most cases the deceased thought very carefully about their will and the people contesting it are not right."
Kim Berrington, head of legacy management at animal charity PDSA, said the charity had noticed an increase in contested wills in recent years. "It seems likely that high-profile cases will further fuel this trend," she said.
Richard Radcliffe, a legacy consultant at agency Smee & Ford, said the RSPCA case would have a mixed effect. "RSPCA supporters might well feel it was rather grabby of the daughter and therefore be more likely to leave legacies in their wills to the RSPCA," he said.
People who were not supporters of the RSPCA, however, would probably say they were "jolly glad" about the ruling and it was about time families fought back, he said.
Radcliffe said contested legacies were sometimes beneficial to charities because when family members found out more about a charity one of their relatives had left a legacy to, they often decided to support it in their own wills. "A complaint is often the best form of fundraising," he said.
Sue Fernley, legacy manager at the RNLI, said she did not believe the RSPCA case would lead to a "rush of people contesting wills".