But after 83 years of prayer breakfasts, Bible study groups and freshers week stalls, the future of the Christian union on university campuses is under unprecedented threat from students who claim that the societies are homophobic and exclusive.

At a time when Islamic militants are accused of recruiting activists at universities across Britain, at least four Christian unions are threatening legal action against their university student unions after being banned or denied access to facilities.

One has been threatened with pickets and its members told that they are “gutter-crawling scum”; another has been accused of “callous and inhumane attitudes” after one of its members prayed for the souls of homosexuals at a prayer meeting.

In a far cry from the serene circumstances in which Norman Grubb, a young Cambridge undergraduate, decided in 1923 to call a meeting of 16 like-minded Christians to his college rooms, the Christian unions claim that their existence is at risk by a secular agenda that opposes their core religious beliefs.

Andrea Minichiello Williams, public policy officer for the Lawyers Christian Fellowship, which is offering informal legal advice to the Christian unions, told The Times she expected a number of legal cases against universities. She said last night: “Christian Unions are facing increasing difficulties in being allowed to function on campus, but they have a fundamental right to speak and to associate around a creed, in this case a Christian creed and Christian beliefs.”

At a meeting yesterday Christian unions at Edinburgh University and the nearby Heriot-Watt University took advice from lawyers about the possibility of courtroom action in an attempt to stop what they claim is a breach of their human rights.

In an unprecedented move, the Christian union at Exeter University announced on Thursday it was giving 14 days’ notice to the students’ guild before starting judicial review proceedings of the decision to suspend it from the list of official university societies. It said it was taking the action to protect “a fundamental issue of freedom of speech and of common sense”.

With the Christian union at Birmingham University also threatening legal action after it was disaffiliated from the students’ guild after 76 years, the prospect of a protracted stand-off between up to 20,000 members of Christian unions across Britain and their student unions was raised.

Peter May, a member of the Church of England General Synod and chairman of the Universities and Colleges Christian Fellowship (UCCF), the umbrella group for Christian unions, spoke this week of “the very difficult position thousands of Christian students are facing”.

He told a meeting of 70 Church of England and Roman Catholic bishops: “If CUs uphold orthodox Christian teaching they can find themselves banned from using campus buildings, their students’ union bank accounts frozen, and removed from the official list of SU societies on campus.”

Tensions between Christian unions and student authorities have been rising since January, when the CU at Birmingham University was suspended by the guild of students after it refused to allow its meetings to be led or addressed by anyone not prepared to sign up to its ten-point statement of beliefs. It also refused to alter its constitution to include references to people who were gay, lesbian, bisexual or transgender.

Although its student guild bank account has since been unfrozen, it has now been struck off the list of official university societies, depriving it of vital funding and free access to room space and publicity. Will Monaghan, a member of the Birmingham CU’s executive committee, said that the group was considering legal action.

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