But millions of offices and homes across the country may be misled into buying up to double the necessary quantity of this precious liquid, according to a Which? survey that said most printers were programmed to suggest that users change their cartridges well before they were empty.

A typical three-colour Hewlett Packard cartridge with a 17ml capacity costs £29. That breaks down to about £1.70 a millilitre. Laser printers, which print faster than the traditional inkjets, were particularly serious offenders in the tests.

Both the Epson AcuLaser and the Minolta Magicolor issue warnings that new toner is needed just halfway through the cartridge’s lifespan. By ignoring the warnings it is possible to achieve nearly double the output.

Epson printers were singled out for particular criticism, with the report claiming that microchips embedded into its ink cartridges stopped the printer from working before the ink ran out.

Using a £20 “chip resetter” tool, which is readily available on the internet, the Which? inspectors were able to override the mechanism and found that the “empty” cartridge printed up to 38 per cent more pages without any visible drop in quality.

A spokesman for the Consumers’ Association, which publishes Which? magazine, said that consumers were being “hard done by”. “With replacement laser toner cartridges costing up to £110 a go, rising to about £300 if you buy the whole set of four colours, it can pay to ignore these warnings.”

Epson said that customers were free to reset their cartridges to get more ink out.

A spokesman for the company said that it would continue to manufacture pre-programmed cartridges “to protect customers from accidentally damaging their printer or producing sub-standard print quality, by unknowingly draining the ink cartridge and damaging the print head”.

Experts from Which? said that damaging the print head was unlikely if consumers stopped printing as soon as they noticed a drop in quality.

Matthew Knowles, spokes-man for the British Chambers of Commerce said: “We are very concerned about this report. Printer ink is a particularly large cost to small businesses and directly affects their competitiveness.

“The firms should be given an opportunity to redress this themselves but if they are unrepentant then there should be an independent investigation.”

An Office of Fair Trading report published last year, criticised the price and performance of inkjet printer cartridges and called for an industry standard. Only a tiny proportion of the discarded cartridges are recycled, with 20,000 tonnes of waste each year ending up in landfill sites.

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