The Scottish Government's claims of falling crime figures have been dealt a serious blow by the UK body that approves key official statistics.

The UK Statistics Authority (UKSA) has refused to rubber stamp the Holyrood Government's recorded crime figures amid claims that police officers had massaged data. The independent watchdog has not endorsed the police figures behind the Government's claim that crime is at a near 40-year low.

The authority's indication that the figures are not meeting its high standards has been described as deeply worrying by opposition MSPs in Holyrood. The body's job is to safeguard official statistics and rule on whether they can be "designated", effectively giving them a pass mark.

In January, the body cancelled the "designation" for crime data for England and Wales after concerns were raised about officers manipulating the figures. Sir Andrew Dilnot, the UKSA chairman, said there was "accumulating evidence" that the figures collated for forces south of the Border were unreliable.

The Sunday Herald has learned that the authority last month decided against "designating" the Scottish Government's own crime figures.

North of the Border, the police provide the Government with recorded crime figures that are verified and published by Scottish ministers.

In the 2012-13 figures, which were part of the assessment, the Government reported that non-sexual crimes of violence were down by 21% and homicides by 25%. Attempted murder and serious assault were also recorded as falling by 22%.

A raft of other figures was presented against the backdrop of the lowest recorded crime stats since 1974. However, the authority has dealt a blow to the credibility of the Government figures.

"We conclude that the statistics do not currently comply with several elements of the Code of Practice," the report noted.

The authority said the Government should obtain "strong levels of assurance" about the quality of the figures, but warned: "This report concludes that the Scottish Government lacks sufficient evidence to be able to provide such appropriate reassurance."

It added: "The authority considers that the Scottish Government has not created, and put into practice, a coherent framework for considering the quality of the underlying data, and does not have sufficient information about the quality of the police recorded crime data."

In the absence of an independent audit, the watchdog concluded: "The authority cannot, at present, confer the designation of Recorded Crime in Scotland as National Statistics."

The report also revealed that the Scottish Government had attended meetings with stakeholders on recorded crime statistics, but no minutes were taken. In its previous assessment, the authority passed the Government's recorded crime figures in 2009.

The authority's move comes months after former police officers told the Sunday Herald that crime figures were manipulated to present a more rosy picture of law and order to the public.

The former officers said some serious assaults, classed as violent crime, were being recorded as "common assault". They also said some robberies were diluted to assault and theft.

Scottish Liberal Democrat justice spokeswoman Alison McInnes MSP said: "It is deeply worrying that the UK Statistics Authority has lost confidence in the credibility of Police Scotland and the Scottish Government's crime figures.

These statistics are often integral to their justification of controversial policies such as the surge in the use of stop and search or the deployment of armed officers on routine patrol.

"People must be able to trust the accuracy of the figures that the national force and ministers quote, and they don't expect them to come with a health warning."

Graeme Pearson, Scottish Labour's justice spokesman and a former senior police officer, said: "The integrity of these statistics is an important confidence issue for the public. If we cannot trust these figures, our trust in wider policing issues evaporates. The steps by the UK Statistics Authority in that light is extremely worrying.

"It is indicative of Justice Secretary Kenny MacAskill's hands-off approach to the justice system. He seems to believe he should be a step away from these matters."

A Scottish Government spokesperson said: "The UKSA has not removed the National Statistics badge from recorded crime statistics in Scotland. This is very different from the situation in England and Wales. Every report from the UK Statistics Authority points to improvements statistics producers can make; this report is no different. We are already addressing a number of the requirements in the report and an action plan will be put in place to meet the rest."

Meanwhile, an authority spokesman said he had nothing to add beyond the report. A Police Scotland spokesperson said: "Official recorded statistics are published by the Scottish Government."