Jerry Falwell Jnr, the controversial Trump-ally and president of Liberty University, is trying to claim his school is still the 'largest Christian university' despite a drop in enrolment.

Grand Canyon University has overtaken Liberty with an enrolment of 111,211 students in 2015-16 compared to Liberty's 109,921.

However Falwell hit back at the claim his Lynchburg-based school had lost the top spot by suggesting GCU was not a real Christian university.

'Our definition of a Christian university only includes universities who hire faculty who adhere to fundamental Christian doctrine. GCU does not. Liberty does,' he said in a statement to the US-based RNS site.

He said that his definition of 'fundamental Christian doctrine' was based on his own school's doctrine of faith.

He added: 'Liberty's definition of a "Christian" university for identification purposes refers to evangelical Christian universities.'

But John Fea, an expert in American evangelicalism and professor of history at Messiah College, suggested the spat was part of a wider debate among evangelicals over whether other branches of Christianity, such as Catholicism and Orthodoxy, were truly Christian.

'Why would you argue over such semantics?' Fea told RNS. 'Why would it be important to claim that you are the largest Christian university in the world other than to use this as a platform for your own theological and, in Falwell's case, political agenda?'

GCU also came back at Falwell and said that while they had 'utmost respect for Liberty and its mission as a Christian university', they disagreed with his slur on their school.

'As a Christian institution, GCU is committed to distinctively Christian approaches toward education that are grounded in theological conviction, development of sound character, and the capacity to live in ways that honour God, benefit others and contribute significantly to the common good,' a statement to RNS said.

Falwell also disputed the metric used, saying that even if GCU had a higher enrolment figure, Liberty had more full-time students with 65,290, compared to GCU's 63,350.

'If GCU requires faculty to affirm a strong Christian doctrinal statement and enrolls more students by total headcount while LU enrolls more FTEs (full-time enrollment students), then it would be fair for both schools to claim to be the largest Christian university in the world,' he said in the statement to RNS.

'In any event Liberty will remain the largest non-profit Christian university in the world and the most prosperous and successful academically and athletically by almost any metric for years to come in our opinion.'