Where a professional indemnity claim arises from both design errors (insured) and construction defects (excluded), the Wayne Tank concurrent causation rule means the policy will not respond if the construction exclusion is engaged by an operative cause. An insurer's 'grant of indemnity', even if qualified as subject to policy terms and based on facts then known, constitutes an admission of liability for the purposes of excess layer attachment clauses. Partial payment by a co-insurer does not extinguish the insured's right to claim against other insurers where the insured's total loss has not been fully indemnified.
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