The similarities and dissimilarities I will list are only in my own experience. I will compare seminars in IPAG Business School and seminars at Greenwich University.
Similarities between French seminars and British seminars
Seminar class has smaller groups than a lecture class. It permits students to ask further questions to the teacher, to work in groups or individuals in a particular project from the subject, to go into the subject in depth.
Dissimilarities between French seminars and British seminars
British seminars has no specific class
British seminars are regrouping from 10 to 20 students from the same lecture (depending on the popularity). There's no specific class with the same students. In IPAG, there are classes, and all students from a class are doing the same subject.
More work groups
British seminars have many group projects compared to French seminars which have more individuals projects.
Videos, articles… to prepare for the seminar
Some British teachers give some previous researchers to do before the seminar. There is no or rarely homework for the next seminar. They post some videos or articles to look whereas French teachers are asking homework after the seminar for the next week.
Attendance is done by the student card
The student card in Greenwich is necessary. To attend a class, students need to register from a scanner their card. A picture and name appeared on the computer in order to control the student. In France, a teacher is calling name by name, the list of the class, to mark the attendance.
A student needs to keep his attendance high because if he fails from few points an exam, the teacher can have a choice to let the student success or fail the subject by looking at his attendance, behavior, previous tests…
In my opinion, French seminars are more enjoyable, it is easier to make friends with people in the same class and to do work project with people having the same schedule as yours.
The British Attendance is faster and permits to the teacher to control the identity.