The NHS could save more than £84m a year if it used a cheap, unlicensed drug to treat people in danger of going blind rather than the expensive one currently licensed and promoted by leading pharmaceutical companies for the purpose, a ground-breaking trial has shown.

Researchers led by Prof Usha Chakravarthy from Queen's University Belfast have finally provided an answer to the controversial question of whether the cancer drug Avastin can safely be used to treat people with wet age-related macular degeneration (AMD), the most common cause of blindness.

Their conclusion at the end of a two-year trial, published on Friday inthe Lancet, is that the bowel cancer drug Avastin – cheap because one dose can be split into many – is just as good for this purpose as Lucentis, marketed by the drug company Novartis for more than 10 times the price. One shot of Avastin, injected into the eye, costs £60, while a dose of Lucentis sells for £700.

Many doctors, first in the United States and now worldwide, have been giving their patients Avastin because of the cost, but Genentech, which developed both drugs, Roche, which markets Avastin for bowel cancer but not AMD, and Novartis, which sells Lucentis, have attempted to stop them, arguing that Avastin is not licensed for this use.

Doctors in Southampton, Hampshire, the Isle of Wight and Portsmouth dropped plans to use Avastin when Novartis made a legal challenge.

The trial led by Chakravarthy found that sight was equally well preserved with either drug – and that giving patients regular monthly injections worked better than less frequent shots. Continuous treatment did cause a higher proportion of eyes to develop a condition called geographic atrophy, which is a thinning of the retina, but that occurred with both drugs. Curiously, fewer of the patients who got the regular monthly shots died than in the group who were treated more occasionally.

The NHS should now look at putting the increasing numbers of people with wet AMD on Avastin rather than Lucentis, the team believes. "The logical thing is to get everybody treatment every month with the cheaper drug," said Chakravarthy.

At least 23,000 people are diagnosed with wet AMD every year and will suffer severe sight loss within two years if not treated. The two drugs have now been investigated for their effectiveness and safety by teams of scientists and eye specialists from 23 hospitals and universities in the UK for the past five years.

The largest recruiting site for the trial was Liverpool. Prof Simon Harding, from the University of Liverpool and the St Paul's eye unit at Royal Liverpool university hospital, said: "Avastin is already used to treat wet AMD in some parts of the UK and extensively elsewhere in the world and also for other eye conditions.

"We recommend that the NHS switch from Lucentis to Avastin and make significant savings to be reinvested in patient care."

The Department of Health funded the trial through the National Institute for Health Research. Nonetheless, the government was not prepared to commit to changing its policy on Thursday night. The Department of Health said it would wait for further findings due in 2014.