The Commerce Commission has been granted leave to appeal a court decision that allowed Southern Cross to acquire Aetna and keep hold of all of its 40,000 policies.

Late last year the commission approved Southern Cross's purchase of Aetna unit subject to Southern Cross selling all of Aetna's policies. The commission said that Southern Cross, the country's largest health insurer would gain a dominant market position by acquiring its closest rival.

However the High Court in Auckland last month overturned the commission's ruling and said Southern Cross wouldn't have a dominant position as the barriers to entry in the market are very low.

While the commission has been given leave to appeal the court's finding, not hearing date has been set.