The Supreme Court has ended a Christchurch widow's bid to overturn a property deal completed by her terminally ill husband, who was dying from liver cancer when he bought 3,000 square metres of central city real estate overlooking the Avon River in 2003. David Parkinson paid $12m for the site, despite that being several million more than he had paid for property in the past and being aware he was seriously ill. The deal ended up costing his family more than $500,000 in a forfeited deposit.

His widow, Lynette, tried to get the $12 million deal overturned, claiming her husband's judgment had been impaired by morphine prescribed to ease his pain.

The High Court, Court of Appeal, and now the Supreme Court have found against Parkinson's firm, Gustav and Co Ltd.

A Supreme Court ruling issued this week said Gustav's claim that the transaction was unconscionable, and should therefore be voided, fell "significantly short of being unconscionable, and awarded $15,000 costs to the defendant, Macfield Ltd.

"His (Parkinson's) customary business acumen had not deserted him," Justice Tipping's decision said.

"He had a rational reason for paying what he knew to be a premium for one of the best development sites left in the central business district in Christchurch."

The judgment said Parkinson was an experienced businessman and property developer.

Although his illness was clearly apparent in physical terms, Parkinson still had a good grasp of business affairs and was well able to look after Gustav's affairs.

"While Macfield knew Mr Parkinson had cancer, there is no basis for any finding that it knew or should have known that Mr Parkinson's illness affected his ability adequately to look after Gustav's interests because it did not," the judgment said.