The next director of the electronic surveillance agency GCHQ, Robert Hannigan, is drawn from outside the world of clandestine operations as a Foreign Office diplomat. Former colleagues said the choice of Hannigan – a former adviser to Tony Blair on Northern Ireland, and currently Foreign Office director general for defence and intelligence – suggested that the government was leaving the door open to reform.

"He's not a true securocrat. He's not one of those people who see public scrutiny as an inconvenience to be avoided," said a former government adviser. "Of the candidates he is the more comfortable with moving to some kind of balance between the demands of secrecy and accountability.

"That said, he is not a big beast of the Whitehall jungle, a large personality who will go into and take the institution by the scruff of the neck. Given the current situation, it's hard to say whether that is a good or bad thing," the former colleague of Hannigan said.

Hannigan rose from being the head of communications in the Northern Ireland Office to running its political affairs department. At one particularly critical moment in the peace talks in 2007, Hannigan helped overcome an impasse between Sinn Féin's Gerry Adams and the DUP's Ian Paisley. The latter wanted an adversarial arrangement with the parties glaring at each other across a table; Adams wanted them sitting side by side, as partners. Hannigan suggested a diamond-shaped table as a compromise.

After serving as Blair's adviser on Northern Ireland, Hannigan took his peacemaking experience abroad, in a British effort to broker a peace deal between the Philippines government and Muslim separatists on the island of Mindanao.

When Gordon Brown took over from Blair in 2007, he made Hannigan his adviser on intelligence and security in Downing Street. Hannigan took up his present Foreign Office position overseeing security, cyberthreats and policy on overseas territories in March 2010.

Announcing the appointment, the foreign secretary, William Hague, said: "GCHQ's world-class work is vital to the safety and security of the United Kingdom. As well as his impressive personal qualities, Robert brings to the job a wealth of relevant experience in the fields of national security, counter-terrorism and international relations."

Hannigan said: "It is a privilege to be asked to lead GCHQ, an organisation which is so central to keeping the people of this country safe. I have great respect for the integrity and professionalism of the staff of GCHQ and for what they have achieved under the outstanding leadership of Iain Lobban."