Human rights lawyer John Scott, QC, claims having one chief constable, instead of eight, makes it easier for the Government to exert pressure on the force. Former senior prosecutor Jock Thomson, QC, claims the police chief could simply become "the stooge" of First Minister Alex Salmond and Justice Secretary Kenny MacAskill.
They have also raised concerns over the investigation of serious incidents – such as that of PC Rod Gellatly who died after a shooting incident at a Glasgow police station earlier this week – which are normally investigated by separate, independent forces.
Mr Scott said: "I have concerns about a single force, especially given the increased potential for undue political influence when it's a single chief constable.
"If the Government decides that particular issues are priorities, such as sectarianism in football, then a chief constable might very well decide for himself it's a good idea to focus on that, but a phone call from the First Minister's office or the Justice Minister could also put him under pressure to do something.
"With eight forces it is much more difficult to influence all eight chiefs – the different forces are pretty independent and do things very differently from each other.
"The principle of separation of powers is an important one. It's very important that we have an independent police force." Mr Thomson, who has already raised concerns over the Government's relationship with the Crown Office, claims a single police force brings similar worries. He said: "I have for some time been concerned about the demise of our criminal justice system and the incestuous relationship between the executive and law officers has had and will continue to have in bringing this about. The creation of the single police force will raise additional concerns.
"Concerns were expressed ahead of the creation of the single police force that no democratic society should allow it as it could result in the chief constable becoming the stooge of Messrs Salmond and MacAskill – we're getting there."
The lawyers also say there is concern over who would investigate serious incidents or complaints within the force, with both suggesting forces outwith Scotland may have to do it. Mr Thomson said: "On the basis that when a complaint is made against a particular police force it would normally be investigated by a separate independent force. Who, post April 1, will investigate such matters, since by then there will be one unified force, no part of which can be regarded as independent?
"Presumably, it would have to be a body outwith Scotland. Interesting – and worrying – times."
The concerns follow warnings of a turf war over backroom staff between the single force and the body responsible for holding it to account, the Scottish Police Authority (SPA), as revealed in The Herald yesterday. Chief Constable Stephen House is said to be "spitting nails" at an apparent bid by the SPA to take over key services.
Mr Thomson said: "What they're fighting about is who is going to be in operational control of the police. The chief constable? SPA chairman Vic Emery? I think not. But Mr MacAskill will provide the answer –his answer."
Both the Scottish Government and a spokesman for the new force said the chief constable and the force will be held to account by the SPA. They also said any serious incidents or complaints will be dealt with under the new wider remit of the Police Complaints Commissioner for Scotland, who will become the Police Investigations and Review Commissioner from April 1.
A Scottish Government spokeswoman said: "The Act sets out clear provisions to ensure separation between ministers and police. The chief constable is directly accountable to the Scottish Police Authority, not Government."