Under the new national partnership agreement, 'Towards 2016', civil service unions have agreed that two out of nine principal officer posts on salaries of over 100,000 can now be filled by open competition.

These jobs are currently reserved as promotional opportunities for employees of the service.

The unions also conceded that one in five assistant principal jobs, which carry a salary of 85,000 a year, and one in six higher executive officer posts on 55,000 a year, can be opened up to the public.

The unions agreed to the move after the Department of Finance said that it was becoming concerned about the greying of the civil service.

"The reforms are needed in their own right, but they are particularly important in view of the ageing of the civil service, " it said.

"The average age of the civil service has risen from 35 years of age in 1985 to 41 years of age in 2005. In 1985, 24% of civil servants were over 40;

by 2005 this had risen to 60%, " Finance warned. "The average age of the civil service is higher than that in the labour force as a whole."

More open recruitment was needed so that the civil service can get the "staff required to advise the government and implement its polices in an increasingly complex and fast-changing society."

Officials noted that, primarily due to a recruitment drive in the 1970s, twice as many staff would retire over the next decade as retired in the last 10 years.

As well as losing a large group of experienced civil servants, the rising number of retirements will increase the government's pension bill, which currently costs well over 1bn a year.

Despite a virtually zero unemployment rate, Finance is unlikely to have any trouble filling these senior civil service positions from the wider workforce.

Last year, the Public Appointments Commission . . .

the recruitment agency for the public service . . . was inundated with thousands of applications for just five civil service positions which were at a lower level than the large number of jobs Finance can now throw open to the public.