Mr Smith's departure was announced in November

Doug Smith will hand over the job to Steven Geraghty on 4 April, but will continue in an advisory role for eight weeks, the government has confirmed.

Work Secretary Alan Johnson announced the departure on 17 November, while being grilled on the CSA's poor record.

It has proved controversial since its inception in 1993 to enforce child support payments by absent parents.

A year after a �456m IT system was brought in, thousands of single parents were still not receiving payments in 2004.

Despite some recent progress, some significant problems remain with the new computer and telephony systems Alan Johnson Work Secretary

In January, MPs said it should be replaced unless it was able to improve its performance.

On Thursday the government said the CSA's performance was improving.

But Mr Johnson said: "Despite some recent progress, some significant problems remain with the new computer and telephony systems."

Payments to the company which provided the computer system were being withheld, he added.

Mr Smith's departure was initially reported as a resignation, and referred to as such by both the Tory and Lib Dem leaders during that day's prime minister's questions.

But officials later said he did not resign but was moving on under civil service rules.

The new CSA chief executive, Mr Geraghty, is a former managing director of the Direct Line group.

He said he was excited to be joining the CSA, but recognised that it still faced "significant challenges".