Hundreds of alleged offences including firearms, drug dealing and child sex crimes had to be dropped by prosecutors last year because police were too late in filing their reports.

More than 850 charges were reported to the Crown Office and Procurator Fiscal Service (COPFS) outwith the statutory time frames, leaving prosecutors no choice but to scrap proceedings.

The figures, obtained under freedom of information laws, show that the number of late reports has increased since the introduction of Police Scotland, rising by 14 per cent since the force's first year of operation.

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Police Scotland argued that it met the set timeframes "in all but a tiny proportion" of charges, however experts within the legal profession called for action to improve reporting procedures.

Thomas Ross QC, former president of the Scottish Criminal Bar Association, described the figures as "extraordinary" and said it was "impossible to understand" why the charges were not reported on time.

Looking in particular at the drug dealing offences, he said officers had 12 months to report, adding: "You catch someone with a bag of heroin, you do a presumptive test and you report it. You don't even need to wait for forensics to come back. You could write the report on a single sheet of A4 paper.

"I don't understand it and I think people will be surprised that you could be caught with a drug like heroin and get away with it because the police take longer than a year to report it."

He added that police appear to have a "laissez-faire attitude" to the late reports and argued that it is not good enough to say it is only a small amount of overall charges.

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Advocate and criminal law specialist Niall McCluskey added that it was concerning so many offences were "slipping through the net".

He added: "You almost get a sense that some of these reports are being left on someone's desk and, because of a lack of resources, being forgotten about and by the time they do get reported to the Crown it's too late.

"This is something both Police Scotland and the Crown Office need to have a good look at."

The Herald first reported the problem of late police reports in 2015, when it was revealed that - between 2008/09 and 2013/14 - almost 4000 charges had to be dropped.

The figures for 2013/14, the first year of Police Scotland, showed that 763 charges were reported too late, compared to 872 last year.

Advocate Brian McConnachie QC, a former senior prosecutor within COPFS, said there was "no obvious reason" why Police Scotland had not made improvements over the last five years.

Referring to prosecution alternatives such as fiscal fines and diverted cases, he said the late reports were "just another example of people who are potentially serial offenders simply not getting as far as prosecution".

The lawyer, who claimed a lack of manpower and resources may be to blame, added: "Even if cases are diverted, whatever you may think of that, at least a decision is being taken by prosecutors. In these cases there can be no action."

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While a large number of the charges are for relatively minor crimes, the figures reveal that there were more than 240 drug charges reported outwith the timeframe last year, as well as more than 40 drink-driving charges.

Other offences also included underage sex with a girl between the age of 13 and 16 and causing cruelty to animals.

Police Scotland said its officers work hard to investigate crime and report individuals to the procurator fiscal.

Chief Superintendent Gary McEwan added: "Efforts and processes are in place to meet the required time limits, which in all but a tiny proportion are met.

"That said, Police Scotland continues to work closely with Crown Office and Procurator Fiscal Service partners to ensure standards are maintained and improved as necessary."

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A Crown Office spokesman said: "COPFS hold regular liaison meetings with the police where improvements which can be made in reporting are discussed.

"When a case is time barred on receipt, this is fed back to the police."