We tried one out. It will go in - just - and the Surefix base makes sure it's secure. The UK version of the base isn't ISOFIX though.
The passenger seat has to be all the way forward. That's ok for us as the wife will be using the MINI normally so no-one has to sit in the passenger seat. Having said that, she still had room when she sat in the passenger side with the baby seat behind so we can both go out in it if needed.
I'm keen to hear from people who have used the Primo Viaggio.
JJP