Gordon Brown last night announced the appointment of his 19th special adviser with the arrival of fellow Scot Stephen Carter in No 10 to act as a fixer and filter between the Prime Minister and his army of lieutenants.

Remarkably perhaps, the two men met only "fairly recently" and the 43-year-old high-flyer only rejoined the Labour Party yesterday after relinquishing his membership when he became the first chief executive of Ofcom, the media regulator, in 2003.

Downing St made clear that Mr Brown was very impressed by Mr Carter's track record and high reputation across Whitehall and the business world. It said he would take up his new role "shortly".

"Stephen Carter is somebody of huge talent and expertise, who will be a welcome addition to the Downing St team," said the Prime Minister's spokesman. "His reputation goes before him," he added.

The PM's new Chief of Strategy will also be his principal special adviser and will attend cabinet as an observer. He will report directly to Mr Brown.

It is clear that Mr Carter will be taking a huge pay cut to enter the heart of government. While he will earn £137,400 a year, this is well below the supposed pay packet of around £500,000 he has been earning as the chief executive of Brunswick, the corporate communications firm.

No 10 emphasised that unlike Alastair Campbell and Jonathan Powell, chief aides to ex-PM Tony Blair, Mr Carter will not be able to order civil servants around. Nonetheless, he will not only be in charge of the fellow 18 spin doctors in Mr Brown's private office but also the 50 or so across Whitehall.

Asked why Mr Carter had been appointed now, the PM's spokesman said it was part of an "evolutionary change", which any organisation went through. However, the move will be seen as an effort to beef up the premier's inner circle after a torrid few months of crises and poor headlines.

Mistakes such as allowing General Election speculation to get out of hand last September led to concerns that Mr Brown needed a broader range of expertise to draw upon.

Last night, Mr Carter said: "It is an honour to be asked to work with the Prime Minister and the Downing St team and I will do my utmost to make a difference to effective government."

Married with a young family, he was born in Scotland and studied law at Aberdeen University. Mr Carter is a member of the college's campaign board, which seeks to bring in funding from the business sector.

In 2006, he left Ofcom and, before becoming Brunswick's head, was hotly tipped to become ITV chief executive.

Last night, the Tories condemned his appointment.

Caroline Spelman, party chairwoman, said: "Gordon Brown should be hiring staff to deliver on his promises, not another chief spin doctor."