English universities are relying on "unbelievable" plans to increase international student numbers by up to 100 per cent in four years as government policy leads to fears of volatility in home student numbers.
Durham University plans for a 97 per cent increase in non-European Union undergraduates between now and 2014-15, while the University of Exeter is planning for a 73 per cent rise in certain areas in the same period.
Senior figures in the sector warn that universities are relying too heavily on unrealistic targets for overseas income in their financial planning.
For 2010-11, English higher education institutions aimed to increase their non-EU student fee income from £2.1 billion (9.6 per cent of total income) to £2.3 billion, according to figures from the Higher Education Funding Council for England.
But in a statement to Times Higher Education, the funding body highlights increased competition for international students between UK universities, and fiercer recruitment battles with other nations.
A Hefce spokesman said this "implies optimism in some of the current growth forecasts".
Les Ebdon, chair of the Million+ group of new universities, said Hefce had used stronger words in informal discussions about future projections.
"Every (institution's) strategic plan includes losses of money on home students and a massive increase in international students. (Hefce) says it is unbelievable. It is unlikely the numbers would increase by the amount people are predicting."
A Hefce spokesman said it would have to wait for universities to formally submit their long-term financial plans - due on 15 April - before it could "provide a comment on the realism of the forecasts".
Fees for home and EU students are limited by the government, which also caps the number of places to control costs to the taxpayer. But fees and places for non-EU students are not subject to such limits.
The highest international fee this year was at Imperial College London, where overseas undergraduates faced annual tuition charges of up to £26,250 in lab-based subjects.
Some universities are worried that home and EU student applications may decline when the maximum fee rises to £9,000 in 2012.
To add to their anxiety, the government has threatened to cut the number of places for home and EU students in a bid to control the cost of the loans system, as many universities propose to charge the maximum fee.
Professor Ebdon said: "If you prevent growth in one direction, it bursts out in another. There is a clear cause and effect."
But in a statement to THE, Shaun Curtis, Exeter's international director, says the university's growth strategy is not a response to domestic concerns but was "outlined in a new internationalisation strategy prior to the announcement of UK government funding cuts. Exeter's recruitment plans are driven by diversity as much as volume."
Dr Curtis says in minutes from an Exeter council meeting on 16 December: "Overall, excluding the Business School, delivery for 2014-15 would require 73 per cent growth on 2010-11 planned (international) numbers."
Without the Business School, the increase is 37 per cent. Exeter wants to host 4,000 non-EU students by 2014-15.
Minutes from a meeting of Durham's executive board, held on 22 February, state: "Undergraduate full-time home student numbers were forecast to decrease marginally over the planning period (2010-11 to 2014-15). Undergraduate full-time international student numbers were anticipated to grow by 97 per cent over the planning period."
A Durham spokesman said: "At present, international students make up approximately 9 per cent of the total undergraduate population. The forecasted increase is to 16 per cent of the total undergraduate population in 2014-15."