Big name hire firms have removed tools from their shelves after safety faults were discovered.
Which? investigators hired wallpaper strippers, circular saws, tile cutters and hedge trimmers from major and independent hire companies and found half of the tools failed laboratory tests.
The equipment was tested for electrical and mechanical safety defects in accordance with British Standards and guidelines from The Institution of Engineering and Technology.
The investigation also recorded whether safety equipment was offered, such as goggles, gloves, ear protectors and circuit breakers.
At Jewson, two out of four tools had faults: the transformer for the tile cutter had a loose earth screw, which increases the risk of electric shock and the circuit breaker supplied with the wallpaper stripper had stray live wires near the earth screw. According to the report, no safety equipment was offered except for residual current devices (RCDs) on two occasions.
A spokesperson for Jewson said: "There was a failure to comply with the correct standards and we are putting measures in place to avoid any recurrence of this in the future, including staff recording that safety checks are carried out. All customers should be offered safety equipment; we are reminding staff of the importance of this."
All three tools hired from Speedy had faults, including a wallpaper stripper with a split hose, meaning hot steam could leak onto the user when it was filled with water.
Brandon Hire also hired out three tools with faults, including a circular saw with a wobbly blade and an unusable leaky wallpaper stripper. On two out of three visits, Brandon offered safety equipment such as gloves and goggles, but only offered an RCD on the third.
Travis Perkins and Homebase's Hire Station both provided two out of four tools with faults, a score matched by the four independents also tested by Which?. Safety equipment was offered once out of four visits to Travis Perkins and twice at Hire Station. None of the four independents offered safety equipment to go with the tools hired they hired out.
Which? Chief Executive Peter Vicary-Smith said: "DIY enthusiasts trust these stores to provide safe, reliable equipment, but half the tools we tested failed our rigorous tests and some could have caused serious injury. We expect higher standards from hire companies. They need to consistently check tools - if the shops we visited had carried out effective basic checks, they would never have loaned out half of the equipment."
Most companies agreed to remove the tools on test from their shelves to investigate further and Which? reported the products of greatest concern to trading standards officers.
HSS Hire was the only company to provide equipment with no safety faults. A statement from the company said: "We take safety very seriously... It is standard policy for our customers to be asked if they require any safety equipment."