As Christian Unions are increasingly "suppressed" on campuses, the Archbishop of Canterbury has criticised the constant persecution from some university guilds.

Dr Rowan Williams said the refusal by some Student Unions to recognise evangelical Christian groups looked like a "fear of open argument".

Writing in the Times Higher Education Supplement, Dr Williams said it was not a crime to hold traditional views.

But the National Union of Students said all local unions were trying to do was curb Christian societies' exlusivity.

Concerns arose when the student guild at Exeter University suspended the Christian union (CU) from its group. The guild said that, by requiring that members sign a form saying they follow Christ, the CU breached equal opportunities and was not open to all.

Student guilds and associations at three universities, Exeter, Birmingham and Edinburgh, decided to suspend Christian groups from membership or use of premises on the grounds that their constitutions or meetings are exclusionary and discriminate against non-Christians and particularly gay people.

Members of the Christian Union have threatened to take legal action against the guild. The CU said it has also had its bank accounts frozen by guild authorities.

It is not a crime to hold traditional values, Dr Williams said in his article: "The danger in issuing sanctions against a body whose views you disapprove of is that it looks like a fear of open argument.

"If disagreement is to be silenced because offence may be caused, that is not good for intellectual life; it personalises and 'psychologises' all conflict of ideas and denies the possibility of appropriate detachment in debating issues."

Dr Williams said that while the views of evangelicals on the issue of homosexual sex may be "embarrassing" to liberal Christians, traditional values should not be compared to holocaust denial or racial bigotry.

"Quite often in discussion of Christian attitudes to homosexuality (and this is often the presenting issue where Christian Unions are concerned), it is taken for granted that any statement that a form of behaviour might be sinful is on a par with the expression of hate."

This means, he said, it is "impossible for a conservative Christian, Catholic or Protestant or, for that matter, an orthodox Muslim to state the traditional position of their faith without being accused of something akin to holocaust denial or racial bigotry".

He added: "To challenge behaviour may be deeply unwelcome and offensive in a personal sense, but it is not a matter for legislative action."

Dr Williams also challenged evangelical groups to look carefully at the expression of some of their beliefs.

"No doubt some Christian Unions might do well to undertake a little hard self-examination about whether their language is vulnerable to proper challenge."

He added: "They may need to affirm more clearly and credibly the distinction between declaring behaviour unacceptable and in effect passing judgment on a whole category of persons."

The director of Share Jesus International, the Rev Dr Rob Frost, criticised the bans which he called "a great tragedy".

He told Christian Today: "The loving, serving and gracious ways in which the Christian Unions have carried out their ministry over the last 80 or more years is to be applauded.

"The fact that they are now being pushed off of university campus property, and out of the mainstream of student life is a great tragedy."