"Tipp-ex for the modern world – just hit 'unprint'"

Dr Allwood and his colleagues estimate it would cost £19,000 to build a prototype unprinter but that the costs would come down as technology improves and it is commercialised

Engineers have developed a way of using lasers to remove ink from paper so it can be reused in printers and photocopiers.

It is a Tipp-Ex for the computer age. Engineers have developed a way of using lasers to remove ink from paper so it can be reused in printers and photocopiers.

The researchers at the University of Cambridge used short pulses of laser light to delete words and images that have been printed onto paper.

The laser vaporises the toner ink without damaging the paper and opens up the prospect of future computer printers and photocopiers having an "unprint" function to allow paper to be reused.

Dr Julian Allwood, who led the research team, said it could drastically reduce the number of trees cut down to produce paper and even provide a cheaper alternative to recycling.

He said: "The process works on a wide range of toners. It does not damage the paper so the feasibility for reusing paper in the office is there."

He added that he has now been approached by several commercial firms expressing interest in producing the first "unprint" devices.

The researchers, whose work is published in the scientific journalProceedings of The Royal Society A, found they could remove toner ink from a range of printers and photocopiers by heating it with short pulses of laser light lasting just four billionths of a second.

They found that while lasers that used ultraviolet light and infrared light were all effective at removing the ink, the most efficient was using a visible green laser.

This removed the ink without causing any physical damage to the paper or discolouration. Filters can be used to capture the vaporised ink, which is given off as a gas.

Dr Allwood and his colleagues estimate it would cost £19,000 to build a prototype unprinter but that the costs would come down as technology improves and it is commercialised.

They calculate that reducing the cost to £16,000 would make the device valuable in most offices by reducing the need to buy paper.

They also believe that it could be kinder to the environment by reducing the need to use as many chemicals to recycle paper and cutting carbon emissions savings of up to 79 per cent.