The RSPCA has lost a High Court battle over a disputed will worth nearly £1m.

The lost case means the animal welfare charity will get a legacy of £370,153 instead of £651,820.

The dispute centred around the interpretation of George Mason’s will, which divided his estate, worth almost £1m, between the RSPCA, his brother John and two friends, Norman and Patricia Sharp.

The RSPCA argued that Mason’s will was constructed in a way which attempted to avoid all recipients having to pay inheritance tax.

Its case was that he bequeathed a total of £300,000 to friends and family, at the time the maximum that could be left in a will without it being subject to tax; with the residue of the estate going to the RSPCA, which as a charity is exempt from the tax.

However, the other recipients believed he wished to leave them his house on top of the £300,000, bringing the sum total to £469,000 and therefore over the threshold for inheritance tax.

High Court judge Mr Justice Peter Smith agreed with the family’s argument and ordered that the £112,000 tax amount be deducted from RSPCA’s residual sum, leaving it with £370,153. Mason’s brother will receive £66,000, while Mr and Mrs Sharp will get £400,000.

In his ruling the judge said: “The claim was extremely weak and should not have been brought.”

He refused the RSPCA permission to appeal because if the case went to the Court of Appeal it would “cause more concern and stress” to Mason’s bereaved elderly relatives and friends.

If the RSPCA had been successful in its case it would have got £651,820. Mason’s brother would have got £28,820 and the Sharps £271,000.

The RSPCA was unavailable for comment.