London transport users applying for an Oyster card online will from today have the opportunity to become organ donors.
Under government plans to increase transplants, people applying for a passport or filing a tax return are also being prompted to help others by donating organs after they die.
More than 600,000 people have signed up to since the trial began on the DVLA website last January.
Grant Shapps, the cabinet office minister, wants all users of government websites to see a reminder to join the organ donation register.
A government spokesman said: “The TfL website provides a great opportunity to reach people living in the capital.”
Mr Shapps said: “Three people still die needlessly every day due to a shortage of organs, something that could be avoided simply by encouraging more people to join the organ donor register.”
Research found that about 90 per cent of Britons said they would donate an organ, but most people were not signed up.
The new drive follows research by the Whitehall “nudge unit”, which found changing the language of donor requests - asking people to put themselves in the shoes of others - encouraged more to sign up.
