Medibank Private has lifted its half-year profit by 6 per cent.

After raising its premiums by an average 4.6 per cent last year, Medibank’s premium revenue has grown by just 1.8 per cent.

But the operating profit for Medibank’s health insurance arm grew by 4 per cent to $243.5 million.

Net investment income fell a surprising 22 per cent to $60 million, which the company says is due to a defensive strategy and lower credit and equity market returns.

Medibank says it is launching a “priority program” to reward long-term customers in response to growing consumer disquiet about ever-rising premiums.

The scheme will see customers who have maintained hospital and extras cover for over 10 years will share in a one-off $20 million bonus from June.

The bonus will come in the form of increased extras limits on services including physiotherapy.

Medibank recently announced it would raise its premiums by an average 3.9 per cent from April - the lowest premium increase in 17 years, but double Australia's annual rate of inflation.

Consumer are leaving premium coverage in droves, with the Medibank losing 50,000 policy holders over the past 12 months.

Meanwhile, its budget ahm brand is cannibalising its parent, with an increase in policy holders growing of 14 per cent, or 340,000 customers.