Christian Unions across Britain are seeking legal advice after four university campus branches were banned from official lists of societies or denied access to university facilities and privileges.

Now Christian Unions at Edinburgh, Heriot-Watt and Birmingham universities are seeking legal advice in the face of accusations that they are excluding non-Christians, promoting homophobia and discriminating against those of transgender sexuality.

The 150-strong Christian Union in Birmingham was suspended this year after refusing to alter its constitution to allow non-Christians to address meetings and to amend its literature to include references to gays, lesbians, bisexuals and those of transgender sexuality.

Edinburgh University has banned an event run by the Christian Union called PURE which promotes a traditional biblical view of personal and sexual relationships.

The university defended the ban, saying that PURE was in breach of its equality and diversity policy because PURE claims that any sexual activity outside heterosexual marriage is not God-ordained. The pressure came principally from the Gay and Lesbian Society at Edinburgh University and follows the university's decision last year to ban copies of the Bible in its halls of residence after protests from the students' union.

The Lawyers' Christian Fellowship criticised the decision to ban PURE, saying, "This incident is an attack on freedom of speech in an institution where an open exchange of views and a search after truth should be strongly upheld.

"In this instance the Christian Union is being denied freedom of expression because what they say and believe is uncomfortable for some groups in the university."

Christian Unions elsewhere are also coming under increasing attack. Christian students are threatening to take Exeter University and students' guild to court over human rights breaches after the university temporarily suspended the Christian Union from the official list of student societies on campus.

The Exeter Christian Union - which has a 50-year history at the university - has also had its Student Union bank account frozen and has been banned from free use of students' guild premises or advertising within guild facilities. Exeter University's student guild claims the Christian Union constitution and activities do not conform to its Equal Opportunities Policies, which have only recently been introduced.

Exeter Christian Union told the university Thursday that it would take legal action after 14 days if it was not fully re-instated as a student society by the guild with full rights and was allowed to call itself the Christian Union.

Emma Brewster, Christian Union worker at Exeter University said: "This is a fundamental issue of freedom of speech and of common sense. Legal action is the last thing we want to take, and we certainly don't relish it, but we are fully prepared to stand our ground for truth and freedom.

"We want to be able to study in a university that allows students - of all faiths and of none - to freely express their views from whatever stance they might take, be able to disagree with one another, and yet to co-exist alongside one another. Surely that is a truly democratic society?

"The Christian Union here, as at almost every university in the UK, holds the orthodox Christian views which churches of all denominations have also held for 2,000 years. In 50 years, this is the first complaint about our name and what we stand for.

"The action currently taken by the guild does nothing to enhance the reputation of Exeter University, or its students to prospective employers, nor does it demonstrate that this university seeks to encourage all its students to freely develop their ideas, thoughts, values and beliefs."

The Lawyers' Christian Fellowship has provided informal legal advice to the students at Exeter but expects a wave of legal action to follow.

"We haven't seen examples of this sort of discrimination against any other groups and we are puzzled by why Christian unions seem to be being singled out," said Andrea Minichiello Williams, public policy officer for the Lawyers' Christian Fellowship in The Times.

Meanwhile, the Universities and Colleges Christian Fellowship (UCCF), the umbrella group for the 350 Christian Unions across Britain, said that the Christian Unions faced a struggle "unprecedented" in their 83-year history.

Pod Bhogal, the fellowship's head of communications, said: "The politically correct agenda is being used to shut people up under the guise of tolerance when, in fact, you tolerate anything other than the thing you disagree with

The UCCF has asked that as many people as possible write to the Principal of Edinburgh University to express their disapproval at the censorship of the Christian Union at the university.