For instance, on the course page for the DPhil in Mathematics at Oxford (http://www.ox.ac.uk/admissions/graduate/courses/dphil-mathematics), they mention the requirement of taking "100 hours of broadening courses before confirmation of status" in the third year of the program. Are these "broadening courses" essentially the same as introductory graduate courses in the US? They involve "submission of written work," so they do not seem like colloquia or seminars.
From Oxford's webpage, Broadening Training,
Courses should be designed to broaden your knowledge and understanding of the Mathematical Sciences as a whole. They should, by definition, not be directly related to the topic of your dissertation ..
And it goes on to list where these courses can come from. I took a look at some of the offerings, and as a US graduate, to me they essentially amount to any approved graduate-level course. Whether you can call them introductory is a bit subjective (course looks cool, ends up nightmare, etc.), but they also confirm that part of these 100 hours of broadening does include seminars and colloquia.