Thousands of immigrants could miss out on British citizenship as a result of cuts to English for speakers of other languages (Esol).
Instead of taking the Life in the UK test, 30,000 people since 2007 have become UK citizens or obtained indefinite leave to remain in the country after taking entry-level Esol and citizenship qualifications.
The courses, which take up to a year to complete, require learners to improve their language skills by a full attainment level from their starting point. They are designed for students whose English skills are not good enough to sit the Life in the UK exam.
But changes to Esol funding - including the introduction of fees for many students and the elimination of programme weighting, which gives extra funding to certain elements of Esol provision - have prompted fears that many of the most vulnerable learners could miss out.
Adult education body Niace has warned that increased Esol tuition fees and a probable drop in the number of courses could prevent many learners from gaining citizenship through this route.
Chris Taylor, Niace's programme director for Esol, said that for students who had displayed a "very impressive commitment" by embarking on a course which could last up to a year, higher fees were the biggest concern.
"With the impact of the cuts that are coming into effect in September, this is likely to become more of a deterrent," she said. "It's certainly an issue for people who don't have very fluent language skills and who can't take the Life in the UK test. When the test was introduced, the intention was to aid integration and help people who show a long-term commitment to life in the UK.
"More would-be citizens will be struggling to fund Esol courses they can't afford. This is a potential barrier to achieving better integration.
"These are learners who need a little bit more support. Learners will be paying for and committing to a course which will take up to a year to complete, and they have to show they have progressed a whole level up from when they were assessed at entry."
Stuart Hanson, director of English Management Direct, which runs Esol courses, said "the most vulnerable of society" would be affected by the changes.
Mr Hanson said learners could be forced to turn to smaller private firms instead of colleges as a result of the cuts. He added: "If colleges aren't providing (Esol), who is? They are less money-orientated than some private providers, which are not very heavily regulated."
A spokesman for the Department for Business, Innovation and Skills said its priority was to "enable people to quickly move into work, targeting help where it is most needed".
"That is why we will fully fund Esol courses for unemployed people on active benefits where English language skills are a barrier to entering employment," he added. "For people not on active benefits and who are settled here, the Government will continue to fund 50 per cent of the costs of Esol."