The taxman’s policy chief Dave Hartnett has been appointed acting chairman of the department.

The appointment of Hartnett follows the sensational departure of Paul Gray over the loss of the personal data of 25 million people.

Hartnett’s appointment to the top post may surprise few in the tax world, where his command of the technical detail has made him an influential policy chief.

But permanent secretaries in such roles often also have experience across Whitehall, which Hartnett does not have.

His appointment to the acting role does not mean he will become full-time chairman, but Gray also carried out the acting role before taking the top spot officially.

Mike Warburton of Grant Thornton said: ‘Hartnett has effectively been the main man and done a cracking good job for a few years. The profession has had a dialogue with the taxman it didn’t have before. He is the best placed man to do it but he would be wasted as the chairman [full-time]. Policy is a much more important job.’

Whitehall sources said his appointment would be welcomed internally, and he is thought to be the first tax inspector to take charge of the department since Sir Norman Price in the 1970s.

The department admitted on Tuesday that it had lost two computer discs containing the bank details of all child benefit claimants.

Chairman Paul Gray tendered his resignation on Tuesday immediately as the news was announced, bringing to an end his brief run at the department and disappointing advisers who had warmed to his style of management.

The astonishing scale of the failures is likely to see an overhaul of the way the government handles personal data.

PricewaterhouseCoopers chairman Kieran Poynter has been called in to look at procedures at the department. There will be a preliminary report next month, with a full report in the Spring.

The responsibility for the failure may also be put down to huge staff cuts that the department has faced, calling into question the cutbacks.