The culture secretary, Tessa Jowell, has extended the deadline for responses to the BBC's controversial Curriculum Online proposal by a fortnight.

Ms Jowell gave commercial rivals until July 22 to assess the BBC's plans after the corporation submitted more detailed documentation on how it plans to work with private companies.

The previous deadline was July 5.

Many privately owned companies that produce education products claim they could face financial ruin if the BBC is allowed to spend £150m of licence-fee payers' money on building a service that rivals their own and is offered free of charge.

The BBC insists its own proposals strongly reflect its public service remit and would provide a valuable service to the UK population.

In an effort to placate private sector rivals, the BBC has pledged to spend 50% of its education funds with external suppliers over the next five years.

"The BBC fully endorses a vital role for commercial players in Curriculum Online," said the BBC in its submission to the Department of Culture, Media and Sport.

Educational publishers have warned the government they could lose up to £400m over the next five years if the BBC is allowed to go ahead with its digital curriculum plans in their present form.

Companies such as Pearson Education, Harper Collins and software firm RM are lobbying for change through the Digital Learning Alliance.

In a recent letter to Ms Jowell, the group claimed the BBC's plan offered little that was distinctive from products and programmes that are already available and would stifle developments in the commercial sector.

The government has said it will make a further £50m available to commercial education firms if the BBC's plans are given the green light. However, the companies said the sum is not enough.