England's NHS IT upgrade does pose clinical risks, but the system will "dramatically" cut the dangers of wrong prescriptions, MPs have been told.
GPs were not consulted well enough, it is claimed
An email leaked to the Observer newspaper suggested managers were worried that some patients were not being entered in the new database.
But Sir Muir Gray, one of the project's directors, told a committee of MPs there were risks with any IT scheme.
He said the benefits of the scheme would reduce other dangers.
He was giving evidence to the Commons public accounts committee, which is investigating the Connecting for Health IT project.
Under the plans, 30,000 GPs in England will be linked up to nearly 300 hospitals by 2014.
It involves an online booking system, Choose and Book, a centralised medical records system for 50m patients, e-prescriptions and fast computer network links between NHS organisations.
It is said to be the most ambitious computer project in the world and represents the largest single investment in IT in the UK.
But The Observer reported concerns among doctors.
It said one of the project's implementation managers in the West Midlands acknowledged in an email in February that the system had failed to record patients' details on a new database.
The manager reportedly said the problem "remains a potentially significant clinical risk".
Asked about the fears, Sir Muir said: "Everything is risk, a balance of risk. There is a risk with all technology but when this is in at minimal risk... this will dramatically reduce the risk of wrongly prescribing, of lab tests and of patient identification."
He said the risks would be addressed throughout the design process and carefully monitored.
The questions session also saw the project's former senior clinical advisor claim that doctors were not consulted enough in its early stages.
Peter Hutton, who was later asked to resign from his post, said people had not been sure what was needed.
"It was like being in a juggernaut lorry going up the M1 and it didn't really matter where we went as long as we arrived somewhere on time," said Professor Hutton.
But Richard Granger, director general of IT for the NHS, said hundreds of doctors were already using the part of the system which had already been delivered.
There had been "massive" consultation, he said, but in any system on this scale there was always going to be a degree of controversy and dissent.
And he said Professor Hutton had previously complained that being open to all clinicians' views on the project would lead to chaos.
'Street by street' fight
The National Audit Office (NAO) last week said parts of the projects were running behind schedule.
NAO chief Sir John Bourn told the MPs he thought the system was likely to be value for money, unlike many government IT projects.
And he thought it would be delivered on time if the NHS accepted his recommendations.
Sir John denied he had been "ground down by a war of attrition" with the Department of Health into producing a "gushing" report.
He said there had been arguments and "proper debate" over his report - but such discussions were not "illegitimate".
But Public Accounts Committee chairman Edward Leigh said the project managers had fought "street by street, block by block" with the NAO.