Favourite British TV shows like Strictly Come Dancing and Broadchurch could be under threat due to a funding shortfall, the BBC is warning.
The rise of services like Netflix and Amazon could mean British content faces "an uncertain future", director general Tony Hall will say in a speech later.
There could be a funding shortfall of £500m over the next 10 years, according to new research.
Lord Hall is to call for a "new golden age for British production".
"The BBC has always shown a great ability to adapt to new challenges and make them opportunities," he will say.
Speaking in Liverpool, he will say if there is an immediate response to the issue, then the future of British content could be protected.
He calls the figures on funding, from consultants Mediatique and published by the BBC, "worrying".
"We have to face the reality that the British content we value and rely upon is under serious threat."
Lord Hall will add that global services like Netflix, Amazon and Apple are not likely to make up the funding shortfall.
"The reality is that their investment decisions are likely to focus increasingly on a narrow range of very expensive, very high-end content - big bankers that they can rely on to have international appeal and attract large, global audiences.
"Even the most generous calculations suggest they are barely likely to make up half of the £500m British content gap over the decade ahead. And a more realistic forecast points to substantially less."
The top five shows in the UK this year so far have all been British - the One Love Manchester concert, Broadchurch, Britain's Got Talent, Sherlock and Strictly.
Lord Hall will say that the BBC "should remain a guardian of UK production", and a "bastion of brilliant British content".
"But to achieve this, we have to recognise that the environment around the BBC has changed dramatically, and we must change in response," he will say.
"In the UK we often think of the BBC as a big player, but today the media market is truly global.
"And in that vast solar system, we are tiny compared to the huge gas giants of the US. And every day they're getting bigger."
While about 83% of independent production companies in the UK were British or European-owned 10 years ago, today that figure is less than 40% - the rest are owned by US multinationals.