Police watchdog is rocked by three high-profile resignations

The replacements of Ms Quinn and Mr Fox-Davis will not be made on a permanent basis, but will continue to be interim posts for the next few months.

Since the inception of the new unified Police Scotland force there has been evident friction between chief constable Stephen House and SPA chairman Vic Emery in what has been portrayed as a turf war.

The consensus last night was Mr Emery was now wounded over the senior departures from his organisation.

Ms Quinn has been in the headlines since her appointment, not least for going on holiday in the run-up to the changeover to a single police force.

News of the departures broke internally with a statement from Ms Quinn, who said she had made the decision to leave in February.

She added: "Due to the length of time it has taken to put the process in place, it will not be possible to have a permanent chief executive in post before I leave.

"We will be looking to appoint an individual to take the reins for an interim period and have them in place before I leave to ensure a smooth and effective handover."

Ms Quinn also acknowledged to staff that there had been "frustrations about the lack of communications from the executive team since day one about the structure and direction of the organisation."

The changes have left SPA staff bewildered and mystified, according to union sources, and words such as "turmoil" were being bandied about by MSPs last night.

While John Fox-Davies's tenure had not been time limited, the reign of Eamon Hegarty as finance director is ending more than a month earlier than scheduled.

Concerns have been raised about who apply to take over from Ms Quinn and Mr Fox-Davis given that the positions will only be filled on an interim basis.

Justice convener Christine Grahame added: "Resignations at these high-level, critical posts and the fact that further appointments will be on an interim basis may give rise to concerns this remains a troubled organisation."

Mr Emery paid tribute to Ms Quinn and said: "As the person who appointed Andrea to the role of SPSA Chief Executive, and latterly also to the interim role in the SPA, I have seen first hand the huge impact she has made to both organisations."

Graeme Pearson, a Labour MSP and former senior police officer, said: "Personally, I'm sorry people have gone. However, if it's the right thing for authority and for the public, so be it."

Scottish Conservative chief whip John Lamont said: "It's a bad start for a new organisation, and the taxpayer will hope to goodness there's not yet another expense as a result of these departures.

"A trio of people leaving right at the top hardly inspires confidence for the future."

A spokesman for the SPA insisted most of the changes had been intimated months ago and that critics were "adding two and two and getting five".

FACTFILE: Trouble at the top

The turf war between Police Scotland chief constable Stephen House and Scottish Police Authority SPA chairman Vic Emery spilled over into public in November last year.

Mr House was said by sources to be angry at a bid by the authority to take over the behind-the-scenes functions for the new single force.

While Mr House feared he was at risk of being made "subservient" to SPA chairman Vic Emery, Mr Emery said he was simply looking for a way to allow Mr House and his team to concentrate their focus on policing.

A subsequently leaked blueprint showed that between July and October the outline for administrative control had altered, shifting from original plans to place everything until Mr House's command to SPA control instead.

Justice Secretary Kenny MacAskill was eventually forced to intervene in January and urged the two sides to share human resources. Finance staff were also assigned to Mr House.

A government file revealed that ministers had found the watchdog's attempts to take over control of all civilian staff "unbalanced and confusing".