The sampling of food to ensure that it is safe to eat has plummeted more than one-third in Scotland over the last four years, as safety inspectors have lost their jobs and public spending has been slashed.

An investigation by the Sunday Herald has uncovered steep declines in the testing and inspection regimes meant to prevent frauds such as horsemeat being sold as beef.

Experts are warning that such scandals could happen again, and politicians are demanding urgent action.

The revelations come as the crisis in the multinational food industry triggered by the discovery of horsemeat in beefburgers continues to escalate.

Last week saw police raids on meat processing plants in England and Wales, three arrests, a string of products being withdrawn by supermarkets and horsemeat in school and hospital food.

A drug known as bute – used to treat horses but banned from the food chain because of its effects on humans – was detected in some horsemeat, and investigations were launched across Europe to try to identify exactly who was guilty of passing horsemeat off as beef. A French company, Spanghero, was implicated by the French government.

As governments, regulators, supermarkets and meat processors struggle to restore consumer confidence, one of the crucial emerging questions is how the public are protected from food fraud and abuse. The answer is that protection is steadily being stripped away.

The number of samples taken by Scottish local authorities to test for food safety has fallen from more than 16,000 in 2008-09 to 10,200 in 2011-12 (see table on page 10). There have been particularly steep declines in North Lanarkshire, Renfrewshire, East Ayrshire, Angus, Aberdeenshire and Highland councils.

According to trade union Unison, the number of meat inspectors in Scotland has fallen by more than 50%, from 170 in 2003 to 75 today. A further five inspectors are facing redundancy with the closure of the Hall's meat factory in Broxburn, West Lothian.

Over the last four years there has been a 21% drop in the number of specialist food safety officers employed by local authorities. A survey by the Royal Environmental Health Institute of Scotland has also revealed an 11% fall in the number of environmental health officers.

The institute's food safety adviser, George Fairgrieve, pointed out that the declines inevitably led to less work being done to protect public health. "A reduction in sampling is just one consequence of the cuts in local authority environmental health budgets," he said.

"A worrying impact of the reduction in the number of inspections being carried out is that the opportunity for fraudulent activities increases and law-abiding traders are disadvantaged."

Although efforts are being made to deal with the horsemeat crisis, Fairgrieve warned that different problems were looming. "There are other vital areas of public health that must also be considered, for example preventing or dealing with outbreaks of E-coli O157 and Legionella," he said.

Professor Andrew Watterson, head of the occupational and environmental health research group at the University of Stirling, argued that the horsemeat fiasco was a "sentinel event" with widespread implications.

"We need to protect public health better," he said. "Declines in meat inspector numbers and local authority food safety officers, along with reduced food sampling, must contribute to a weakening of public health standards and the possibility of criminal abuses in the food system."

He also criticised Government ministers for trying to heap the blame on food processors when it was their responsibility to safeguard public health, saying: "We need to revive, not marginalise, environmental health and food safety and raise standards of protection for consumers."

Unison's Scottish organiser, Dave Watson, accused governments of forgetting the lessons learned from the BSE crisis in the 1990s about controlling the meat industry.

He said: "Only strong, independent inspection can properly protect the public from industry malpractice.

"The current scandal follows cuts in meat inspection and environmental health services, proving that 'light touch' regulation has been a disaster for consumers."

Politicians weighed in with demands for ministers to make an urgent statement to the Scottish Parliament. The cutbacks in sampling and staff were "damning", according to Green MSP Alison Johnstone.

She said: "This scandal is pulling back the veil on an industry that has steadily been left to regulate itself as the cuts hit important public services like the inspection of food. The lack of regular inspection has led to a reactive frenzy of government press releases when what we really need is a properly funded inspection regime."

Claire Baker MSP, Labour's shadow environment secretary, described the cutbacks as "worrying". She added: "The scandal of processed meat over recent weeks has raised many questions, including whether the

regulatory system is robust enough."

But local authority umbrella group Cosla maintained that Scotland's environmental health service was doing an "excellent job" despite councils' worsening finances.

Cosla's president, David O'Neill, said: "The sampling of food by Scotland's environmental health officers has continued. Scotland's councils are committed to excellence in all their services, including the standard of food served to those within their care.

"We will continue to monitor the current situation in regard to the authenticity of meat products and keep our stakeholders informed."

The government's Food Standards Agency (FSA), which has been at the centre of the horsemeat storm, accepted that there had been a fall in food safety sampling in Scotland. But it blamed a 2006 change in European legislation.

There had been a shift away from enforcement and testing by regulators to a system in which food businesses had to demonstrate effective food safety management, said an FSA spokeswoman.

She said: "The legislation requires sampling to be risk-based and targeted towards the production of non-compliant foods. It does not prescribe levels of sampling for official control purposes."

Sampling was still an important tool and the FSA supported local authorities in developing a risk-based approach, the spokeswoman added. But she said: "Whilst the FSA is the UK competent authority for the implementation and monitoring of feed and food law, it has no direct control over sampling budgets, activities or laboratory testing services contracted by local authorities."

The FSA gave Scottish local authorities £166,000 in the current year to enhance levels of surveillance of food and animal feeds in areas of increased risk. It also worked with councils through the Scottish Food Enforcement Liaison Committee.

The Scottish Government said it had nothing to add to the FSA's statement. Ministers announced last June that they wanted to set up a new food safety body in Scotland to replace the FSA, whose role has been reduced by Westminster, but a consultation paper promised in 2012 has yet to be published.