Primary care trusts and GP practices will be asked to correct widespread mistakes on the Department of Health's flagship NHS Choices website.
Half of the website's information on GP opening hours and a third of practitioners' names are thought to be incorrect, HSJ can reveal.
The Information Centre for health and social care made the estimate after a survey of 4,500 practices showed wide variations in data quality on the site, run by Dr Foster Intelligence.
The centre will ask PCTs to review practice lists to improve accuracy. PCTs and practices will be asked to directly change information on the website from later this year.
The developers of the website, launched to give patients information on services and conditions, said data had been directly transferred from the now-defunct www.nhs.uk.
NHS Choices involvement and external affairs lead Jonathan Carr-Brown said the sample showed 'opening hours are accurate for only half of GP practices and practitioner details are accurate for around two-thirds'.
Mr Carr-Brown said the only way to ensure the data was accurate was to 'combine the efforts' of the Information Centre and NHS organisations. There will be a web-based form which GPs and other health professionals will be able to 'update while they are literally having their lunch break'.
This will be available to GPs from October. 'GPs and trusts need to realise they have a part to play in this and we need to realise that our part is to give them a mechanism for doing it quickly.'
NHS Alliance chief officer Michael Sobanja said PCTs would be disappointed at being asked to cross-check the website.
'It would have been a damn sight better if it had been accurate in the first place, ' he said.
Patients Association vice-chair Michael Summers said: 'Clearly it is going to affect patients; they are going to be substantially misled and have their time wasted.'
He said the£3.6m start-up costs and£10m a year running costs were 'an even greater reason for the information to be accurate'.
British Medical Association GPs committee chair Dr Laurence Buckman said family doctors should change incorrect details.
He warned: 'Some GPs will bother and correct it and others will say 'I can't be bothered' and not do that.
'It doesn't surprise me. There hasn't been a government-controlled IT launch that has gone well and this has been no different.'