The PSNI is facing a leadership vacuum with the departure after seven years of Sir Hugh Orde, unionists have warned.
The end of the Orde era also comes as policing faces huge hurdles, not least the transfer of criminal justice powers to the Assembly.
Former Police Ombudsman Dame Nuala O’Loan said Sir Hugh’s legacy would be a positive one.
Dame Nuala, who crossed swords with Sir Hugh over inquiries into the Omagh bomb investigation and again over the role of an informer in a high-profile murder, added he had set a high standard for his successor.
“I think he brought many things. I think he brought a modern vision of policing and how policing could be in Northern Ireland,” she said.
“I think he brought courage, I think he brought integrity and I think he brought enormous leadership skills which enabled him to model the business of saying sorry when things went wrong.”
DUP Junior Minister Jeffrey Donaldson said while Sir Hugh was to be congratulated on attaining an important position in UK policing, “this couldn’t have come at a more difficult time for policing in Northern Ireland”.
And he said it was essential that Sir Hugh’s successor has experience in dealing with counter-terrorism, whether on the UK mainland or in Northern Ireland.
“There is a high level of threat from various terrorist groups and it is essential we have strong leadership at the helm,” the Lagan Valley MP said.
Ulster Unionist MLA Basil McCrea said the decision was not unexpected but will cause some severe difficulties for the Policing Board and policing in general.
“We will now need a new Chief Constable, a new deputy chief constable and possibly assistant chief constable, all of which leads to a new command team in the face of renewed terrorist threats,” the Policing Board member said.
Sinn Féin Policing Board member Alex Maskey said that while Orde has made a significant contribution to many changes, transforming policing had never been about individuals.
“His departure, along with other senior officers who have indicated they are intending to move on, provides an opportunity for the Policing Board, under its new leadership, to put in place a new and dynamic group of officers at the top of the PSNI to manage the next stages of policing transformation which will occur with the transfer of powers,” the Sinn Fein MLA added.
SDLP Policing Board member Dolores Kelly said: “Our highly accountable police service is now vastly different from the force that Hugh Orde took over. When he came, support and participation from the nationalist community was minimal and strained. Now, 26% of officers are from that community and no part of our society is deprived of the services of the PSNI.”
Alliance leader David Ford said: “Sir Hugh has done a magnificent job in his seven years as Chief Constable, during which time there has been large strides forward in achieving confidence from all sides in the police.”
Reaction to the announcement was national and international. Secretary of State Shaun Woodward said: “It is to his immense credit the Police Service of Northern Ireland has developed into one of the most respected police services anywhere in the world.”
American consul general Susan Elliott said: “His stewardship of police reforms and determination to combat criminal activity has won him deep respect at the highest levels of the US government.”