Fellow spokesman Jim Parton said Mackay was the first port of call for journalists looking for case studies on parents going through difficult custody battles, and would 'be sorely missed from media contact books'.
Mackay gave up a career in chartered accountancy to work at the charity after undergoing a family break-up.
Parton said he had 'an irreplacable grasp' of the legal and political issues surrounding child contact cases.
The charity helps parents of both sexes maintain a relationship with their children during family break-ups and provides support during court proceedings.
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