A party to a services agreement calculated by reference to taxable income cannot make extraordinary tax-deductible expenditures (such as a large charitable donation) for the purpose of reducing the other party's contractual entitlement, even where the express terms of the contract define the calculation by reference to taxable income. The implied duty of cooperation at law may prevent such conduct as 'seriously undermining' the contractual benefit. However, the scope of this implied duty remains contested — McLeish JA's dissent holds that the duty must be anchored to express contractual promises and cannot create obligations beyond what the contract requires.
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