More than 40,000 people across the UK have been caught in a backlog of applicants hoping to be invited to citizenship ceremonies.
Prince Charles and David Blunkett at the first ceremony in February
A confidential Home Office document seen by the BBC reveals fewer than 5,000 immigrants have been made British citizens at the ceremonies.
They were launched in February in Brent, London, by the Prince of Wales and Home Secretary David Blunkett.
London accounts for a third of the backlog, the document show.
People applying to become UK citizens since 1 January 2004 have had to pay a fee and pledge to uphold the UK's rights, freedoms and values in a ceremony held at a register office.
Previously people becoming British citizens swore an oath of allegiance in front of a solicitor.
About 90,000 adult applicants are successful each year in their bid to become British, but only 4,922 people have so far attended one of the new ceremonies, with 40,560 adults across the country on the waiting list.
A Home Office spokeswoman admitted that there had been delays in the applications process.
One of the reasons was that more than half of all applicants had sent in incomplete forms, she told the BBC Home Affairs Correspondent Sally Chidzoy.
A change in the fee structure introduced in January may also have added to the confusion, the spokeswoman said.
Lord Tope, of the London Borough of Sutton's Registration Service, which is responsible for the ceremonies, criticised the treatment of applicants.
"The government launched these citizen ceremonies with a great fanfare to welcome new citizens and remind them of their rights and responsibilities," he told the BBC.
"But it seems to have done nothing to prepare for its responsibilities to our new citizens.
"They must now be feeling very unwelcome. The home secretary must act urgently to sort out this shambles."