Chief constable, Strathclyde Police
Mr House, who has been in his current role since 2007, is considered a favourite to lead the Police Service of Scotland. He has also served as an assistant commissioner of the Metropolitan Police and was one of the four candidates shortlisted to become commissioner of that force last year.
Chief constable, Grampian Police
Mr McKerracher, who was fiercely critical of the single force plan, was the first officer to reveal he would definitely go for the job. He said: "Mr House needs to be challenged and I am keen to do that." An officer since 1974, he worked at Strathclyde, latterly as deputy chief constable, until joining Grampian in 2004.
Sir Hugh Orde
President, Association of Chief Police Officers
Sir Hugh, who began his policing career with the Metropolitan Police in 1977, is a former head of the Police Service of Northern Ireland, serving in that role between 2002 and 2009. He also narrowly missed out on the job of commissioner of the Metropolitan Police last year.
Chief constable, Tayside Police
Ms Curran has been in her current role since February 2010 after serving for a year as Tayside Police's deputy chief constable. She had joined Greater Manchester Police in 1988 and went on to become assistant chief constable, taking on responsibility for the force's counter-terrorist unit.