Belfast Islamic Centre’s Raied Al-Wazzan was the first person to lodge a complaint about Pastor James McConnell’s sermon criticising Islam

The Public Prosecution Service is behaving in an "authoritarian manner" and is undermining freedom of speech by prosecuting Pastor James McConnell for his comments on Islam, the National Secular Society has said.

The society has written to the Director of Public Prosecutions (DPP) Barra McGrory raising "serious concern" and legal questions about the decision to prosecute the firebrand evangelical preacher.

The Belfast Telegraph yesterday revealed that the main witness in the prosecution case is set to be Dr Raied Al-Wazzan of the Belfast Islamic Centre, who earlier this year praised Islamic State for being a positive force in Mosul, his home city in Iraq.

Pastor McConnell potentially faces up to six months in prison if convicted over a sermon last year in which he branded Islam "heathen" and "Satanic". In his PSNI witness statement, Dr Al-Wazzan denounces the pastor's "terrible comments" which he finds "offensive and disgusting".

The Belfast Telegraph unsuccessfully tried to contact Dr Al-Wazzan for comment at the Belfast Islamic Centre yesterday.

The London-based National Secular Society (NSS) is the latest in a growing number of religious and non-religious groups to oppose Pastor McConnell's prosecution. A coalition of moderate Muslim, Christian and atheist figures have joined together to support the evangelical preacher's right to free speech.

In a letter to Mr McGrory, the NSS's executive director, Keith Porteous Wood, said the case against the pastor was not in the public interest.

"Given there seems to be no incitement to violence in McConnell's comments, the PPS must be seen to have behaved in an authoritarian manner and, at a critical time, to have undermined freedom of speech in a period where it is already under very direct attack.

"The prosecution must be viewed in a broader context where freedom of expression is being curtailed, particularly with regards to Islam and the criticism of religion.

"We question whether your decision would have been taken were Islam not the subject of the 'offending' aspects of his sermon. If the word 'atheism' were substituted, we find it extremely improbable - even unimaginable - that the PPS would have pursued this reckless course of action."

Mr Porteous Wood added: "Criticism of ideas and ideologies must be considered as protected speech in the most fundamental sense, and James McConnell was exercising this right as he is, in our view, completely free to do."

Pastor McConnell has been charged under the 2003 Communications Act with "sending, or causing to be sent, by means of a public electronic communications network, a message or other matter that was grossly offensive".

The charges centre on a sermon he gave in May 2014 in which he said "Islam is heathen, Islam is Satanic, Islam is a doctrine spawned in Hell." The sermon in the Whitewell Metropolitan Tabernacle was streamed on the internet.

Mr Porteous Wood claimed the PPS's decision to bring charges were "a serious misreading" of the Communications Act and "a gross overstep of that legislation's intent as framed by parliament".

He said: "The prosecution in itself, irrespective of the trial's outcome, has created a chilling effect already as evidenced by the view of the Evangelical Alliance and the response of churches.

"The Reverend Brian Lacey, of St Peter's Church of Ireland in Belfast, described the law in this area as a minefield and said he would not wish to place his sermons online. A successful conviction would be a significant and regressive moment."

Mr Porteous Wood said the PPS must "fully consider human rights legislation and apply the principles contained in the European Convention on Human Rights".

He added: "In light of this we urge you to reconsider your decision. It is not in the public interest to pursue a case which is so palpably harmful to religious freedom and the fundamental right to freedom of expression."

A spokeswoman for the PPS confirmed it had received the National Secular Society's letter and said it would be "responding in due course".

She added: "This case is now before the court and it is for the judge to decide on all evidential matters. It would be inappropriate for the PPS to make any further comments at this point."

Last month, Dr Muhammad Al-Hussaini of the Westminster Institute, a practising Muslim, spoke out against the decision to prosecute Pastor McConnell. He described it as "extraordinary" and "contrary to our country's tradition of freedom of speech".

He added: "I strongly uphold the moral right of Pastor McConnell and myself, as Christian and Muslim, to disagree about matters of doctrine and belief."

Belfast Telegraph