Substandard surgical tools from Pakistan are putting UK patients at risk of potentially deadly injury and infection, BBC Panorama has found.
Faults include rough edges, steel burrs that can splinter during operations and corroded metals.
All surgical instruments have to meet regulatory standards but only one of the more than 180 NHS trusts and boards conducts rigorous tests on every tool.
Barts and the London NHS Trust reject almost 20% of tools as unsafe for use.
Tom Brophy, the dedicated technologist at Barts, said the prevalence of faulty equipment that could endanger patients' lives or cause serious injuries is so worrying that he has started documenting the faults.
While he is able to return unsuitable or faulty tools to suppliers, he said there is nothing to stop those same instruments from being sold on to another UK hospital, either within the NHS or private.
"On more than one occasion a supplier has rung me up and said that the instrument you rejected, I passed it onto another hospital and they accepted it," he said. "Of course they're going to accept it, because they haven't checked it."
While most hospitals carry out some degree of visual checks on instruments, only Barts employs a dedicated technologist.
Poor quality surgical implements have been identified as a likely cause of MRSA infections because shards of steel have caused microscopic holes in surgical gloves.
Badly made instruments that have unwanted grooves or trenches can trap body tissue and fluids - another possible source of infection.
All of the 916 companies making or supplying surgical instruments in the UK must be registered with the Medicines and Health Care Products Regulatory Agency (MHRA), but responsibility for quality rests with suppliers and manufacturers.
Neither the NHS or the MHRA requires suppliers to inspect manufacturers.
In a statement, the MHRA said "it has no evidence that non-compliant instruments are being supplied to the NHS", but added that if there were such evidence, it had "a range of powers and sanctions available to deal with the problem".
In addition to rejecting poor quality equipment that is sold to Barts, Mr Brophy said he has been sent used equipment - with traces of blood still on the instruments - being passed off as new.
Two-thirds of the world's surgical instruments are made in the city of Sialkot in northern Pakistan and 70% of the UK's registered manufacturers are based in the city.
While some of the larger companies operate state-of-the art facilities and have rigorous quality-control procedures in place, Panorama found evidence of smaller firms that do not use magnifying glasses to inspect finished instruments before putting the required quality stamp on them.
Others outsourced manufacturing to some of the 3,000 back-street workshops in the city where undercover filming revealed a complete lack of hygiene or quality control.
Professor Brian Toft, a government adviser on patient safety, said if procurement officers in both the NHS and private hospitals in the UK knew of the conditions in which the surgical instruments were being made, they would "faint at the thought of it".
"I cannot believe that anybody in the NHS knows this is going on," he said.
Panorama: Surgery's Dirty Secrets, BBC One, Monday, 27 June at 2030 BST and then available in the UK on the BBC iPlayer.