The Tories have accused the government of cronyism after it was announced that a colleague of Cherie Blair is set to become director of public prosecutions.

Ken Macdonald QC, a founding member of the Matrix chambers, will replace Sir David Calvert-Smith in November.

His appointment was determined by a panel comprising of Sir Hayden Phillips, permanent secretary at the Department for Constitutional Affairs, Cabinet Office chief Sir David Omand and Lord Justice of Appeal Sir Robin Auld.

The committee was chaired by Baroness Usha Prashar, the first civil service commissioner.

But shadow deputy prime minister David Davis described the appointment as "rampant cronyism".

"Many people will find this appointment astonishing," he said.

"We have already had one lord chancellor who was the prime minister's boss and the current one who is his former flatmate.

"Now we learn that the new director of public prosecutions is a founder member of the same legal chambers as the prime minister's wife.

"Under this government there appears to be no institution which is safe from the prime minister's rampant cronyism.

"There are certain parts of the British constitution that should be totally protected from this kind of behaviour and paramount among these should be the judicial system that only two months ago the prime minister claimed he wanted to free from all forms of political interference."

Liberal Democrats described the choice as "provocative."

"I have no reason to doubt that Ken MacDonald is up to the job, but this is a provocative appointment and we will need assurances that the decision was impartial and based entirely on merit," said home affairs spokesman Simon Hughes.

"This is becoming more and more a government of who you know rather than what you know.

"Whether or not it is intended, jobs increasingly appear to go to people who are 'one of us'."

Macdonald has chaired the Criminal Bar Association and served as a part-time Crown Court judge since 2001.

"This is obviously one of the most challenging and exciting posts in the criminal justice system and I am very much looking forward to taking it on," he said.

"I am also delighted to be joining the Crown Prosecution Service at this crucial period in its development."

"I agree with the attorney general and Sir David Calvert-Smith, the present DPP, that it is time for prosecutors to take their proper place at the heart of criminal justice," he added.

"We shall release the full potential of the immense reservoir of talent that is to be found within the CPS, and we shall place it at the disposal of the community.

"A transparent, fair and effective prosecuting authority is one of the hallmarks of a great liberal democracy. This is our aim."

Despite the opposition criticism the appointment was welcomed by attorney general Lord Goldsmith.

"He brings to the job a distinguished record in the criminal law, strong leadership qualities and a commitment to a firm and effective CPS, prosecuting in the public interest," he said.

"He will oversee the introduction of the charging proposals in the Criminal Justice Bill, which in pilots have led to a 15 per cent increase in convictions.

"I look forward to working with him to continue the reform of the CPS and to enhance the role and status of prosecutors."