Marsh now alleges it lost 13 clients after former SA manager of strategic risk Noel Vickery left the company and joined Arthur J Gallagher.

Five of the clients – including the SA Master Builders Association – account for about a third of Marsh’s alleged losses. 

The Federal Court last week allowed the company to amend its claim against Mr Vickery and add the five to a list of clients that left after he was made redundant.

Mr Vickery worked for Marsh between 2004 and February 2012, and went to Gallagher later that year.

Justice Anthony Besanko says Marsh alleges Mr Vickery used information about the company in breach of his obligations to it. A number of Marsh clients have switched their business to Mr Vickery and Gallagher, causing Marsh to “suffer loss and damage”.

Marsh started action against Mr Vickery in December 2012, when it alleged it had lost seven clients. It has since added clients that switched last year.

Justice Besanko says the latest application to update the list comes up to two years after Marsh became aware it had lost the SA Master Builders Association business, but he is satisfied the company “will suffer fairly substantial prejudice if the amendment is not allowed”. 

A trial date has not been set.