The number of overseas students wanting to attend UK universities could triple to more than 870,000 by 2020, a report predicts.
Universities are vital for the economy, the British Council says
The British Council said this would be worth around £13bn a year to the economy, but warned of competition from abroad, including the US.
UK universities required "significant investment" to avoid a fall in their global market share from 30%.
The largest predicted growth in demand is from China, from 20,000 to 225,000.
Currently, around 270,000 foreigners are studying at UK universities.
They pay £1.5bn a year in fees and contribute £3bn to the economy.
International students - from non-European Union countries - pay full-cost fees and some universities are now increasing overseas recruitment to balance financial losses for British students.
The British Council says competition is growing fast from universities in Europe, India, and the Far East.
Britain is second only to the USA in the international student market, which is expected to treble to 5.8 million by 2020.
The number looking for courses in English-speaking countries is predicted to expand from one million in 2003 to 2.6 million by 2020.
'High quality is essential'
David Green, director general of the British Council, said: "The UK's position in the market and the added value to the economy is at risk if we do not continue to invest.
"This is essential to underpin the gains already made, to combat the increasing competition from countries such as the US, Australia, Malaysia and Singapore, and to ensure high quality in the provision of education."
According to the council's figures, the UK accounted for 24% of the market for overseas students in English-speaking countries last year.
In its worst-case scenario of under-investment and poor value compared with competitors, this would fall to 10% by 2020.
In its best-case scenario of high investment and competitive pricing, this would rise to 33%.
France, Germany and the Netherlands are already offering postgraduate programmes in English.
UK institutions, meanwhile, provide higher education courses for 190,000 students in their own countries.
Professor Ivor Crewe, President, Universities UK, which represents vice-chancellors, said: "International students make a significant investment and place their trust in us when they decide to come to the UK for their higher education.
"We recognise the critical need to maintain and build on the reputation for quality higher education that is the key factor in the UK's success in educating citizens of other countries."
Phil Willis, education spokesman for the Liberal Democrats, said: "If overseas student numbers rise to a projected 870,000 by 2020, the equivalent of 62 universities would be needed to accommodate the influx of students - with additional demand for accommodation.
"If not enough places are made available, UK-based students will lose out to their higher fee-paying international counterparts.
"With the introduction of top-up fees in 2006, a massive increase in fees will be the only way universities can cover the additional cost."
A spokesperson for the Department for Edcuation and Skills said: "We have every intention of remaining one of the most popular destinations for overseas students . That is why we launched the prime minister's initiative in 1999 to recruit an additional 50,000 international students by 2005."
UK higher education institutions had exceeded that target already, she said.
"The Higher Education Bill is designed to strengthen our universities, by providing them with an independent source of additional funding, which will help make them stronger in an internationally competitive market."