The reputation of the UK PhD could be undermined by too great an expansion of professional doctorates, according to international experts.
At an energetic debate at the Vitae conference in Manchester last week, Barbara Evans, dean of the faculty of graduate studies at the University of British Columbia, said respect for the US version of the qualification had already been lost.
"There are too many taught doctorates," she warned, adding that the doctorate was no longer seen as the "gold standard" in the US.
European universities need to "be careful" and defend the values of the doctorate, she said, adding that it was up to UK institutions to ensure that the qualification retained its crucial research component.
Thomas Jørgensen, senior programme manager for the Council for Doctoral Education within the European University Association, said other European Union nations were reluctant to follow the UK's lead.
He described professional doctorates as "a very British thing".
"My feeling is that across the Channel, they will say, 'we don't need to do that'. I don't know if it's a good or bad thing for the UK, but I don't think the model will be copied," Dr Jørgensen said.
Janet Metcalfe, head of Vitae, said comparisons between UK and US taught PhDs were unfair. In the US, some of the qualifications are entirely taught and are poorly regarded, but the UK taught PhD includes a major research project lasting at least two years.
"If we use the term 'taught doctorate', we will be seen as delivering doctorates without any research component at all. We need to stop using that language," she warned.
Geriant Johnes, dean of postgraduate studies at Lancaster University, said that the evolution of the PhD was important.
"The reality of doctoral training is changing," he said. New versions offer choice and also reflect "changes to the nature of some of our disciplines as knowledge advances".
But a barrier to a well-regarded UK professional doctorate is the lack of enthusiasm from potential thesis supervisors, he added. "I find it very difficult to persuade my colleagues. Supervisors fear that they cannot publish through working with a professional candidate, and so they don't want to engage."