The relationship between Islam and European identity clouded a robust debate tonight as audience members and panellists clashed over the future of the European Union.

The discussion, hosted by think tank Theos, focused on a vision of what Europe should look like and coincided with the launch of a report entitled "A soul for the union". Author Ben Ryan argued that in order for the EU to survive, it must "discover a soul".

The EU must have "its own identity and moral mission" rather than just existing for economic ends, Ryan said.

However questions of faith and European identity proved controversial as Dr Dave Landrum, head of advocacy at the Evangelical Alliance, asked whether it was possible for Europe to survive without its original Christian identity.

Europe was initially defined as being non-Islamic, said Landrum in an audience question.

A number of audience members objected to the statement including Andrew Brown, author and religious editor at the Guardian.

"It is really extraordinary to see Dr Dave Landrum defining Europe to exclude Muslims," he wrote on Twitter.

However Landrum defended his comments and insisted what made European identity distinctive was "obviously Christianity".

"Unless the European parliament acknowledges its Christian identity in some way, it is bound to fail because it is running against the grain of history," Landrum told Christian Today after the debate.

"The EU has departed from its own identity," he added. "Unless it embraces its essential identity then it won't be able to integrate and engage moving forward."

Brown was contacted for a comment but did not respond.

However Ryan told Christian Today that Landrum was "right in a sense".

"It depends how you understand what it means to be European," he said. "What defines Europe is an intellectual space – it's an idea. That idea has historically always been a mixture of Greek philosophy and Christianity.

"That is its history and is never going to go away," he said. "However other people can join in."

The distinguished panel included Sir Simon Hughes, former leader of the Liberal Democrats and Dr Helen Szamuely, head of research at the Eurosceptic Bruges Group. They discussed a number of topics surrounding the upcoming referendum on Britain's membership of the EU, including national sovereignty and the purpose of the Union.

Hughes, an open advocate for Britain's continued membership of the EU said: "Because I believe in a generous God who loves all people equally I believe we should not be selfish. I passionately think we should work closer together with EU."

"We haven't lost sovereignty, we have just shared sovereignty," he said. "That is actually a gain of sovereignty."

However Professor Brendan Simms, founder of the Project for Democratic Union, went further and argued for "one single state" as the only practical solution.

"The EU speaks to deep yearning in continental Europe," he said, arguing that it was cultural differences that made a single super-state even more imperative.

Szamuely was more sceptical and said her vision was of a "network of individual states". She argued that freedom wasn't possible in a system of large centralised government.

The wide range of visions expressed, both for Britain's continued membership and for its exit, reflected the complex nature of this debate and the difficulty both sides have in making their case coherently.