GWENT'S health board is warning that it will need to close an eyewatering budget gap of at least £100 million during the next three years, in order to balance its books.

The sobering estimate of the financial challenge facing Aneurin Bevan Health Board is reported in its medium term plan.

And the plan cautions that the estimate is based on a number of assumptions regarding issues like the costs of drugs and Continuing Healthcare, the treatment needs of the population, and on the health board breaking even this year.

On that basis, the estimate of the financial challenge to the end of 2016/17 is put at just over £107m.

But the report states: "This is considered a conservative estimate when compared to previous years, and with other health board peers. It is therefore important to note that the scale of the financial challenge may be materially greater than this assessment, but is unlikely to be lower."

That £107m is assessed as being around four per cent of the total expenditure over the three-year period 2014/15, 2015/16 and 2016/17.

One factor that could make the figure even greater however, is if the health board fails to break even this year. Currently, it is forecasting an overspend for 2013/14 of £5.6m, which if previous arrangements were followed would require it to borrow the deficit sum from the Welsh Government, repaying it the following year.

Issues such as wage awards and the fluctuating costs of agency and locum staff could also have in bearing over the size of deficits in the next three years.

But the health board is that ongoing root-and-branch reviews and reorganisations of services and work patterns will help deliver the savings required to bridge the budget gap, while acknowledging that the challenge is huge.

Major shake-ups in the way key services such as A&E, neonatal, paediatric and obstetrics are provided will be announced next week, and these could help reduce costs, but even more wide ranging changes in the way the NHS in Gwent operates will be required.

The health board has already, over the past five years, saved more than £150m in order to cope with the financial challenges of shrinking NHS Wales budgets.