Is there any technical as well as practical differences between the two academic positions, one being a permanent faculty position in the UK (or Australia/NZ and other similar systems) and the other being a tenured position in the US/Canadian universities? I believe most things may come down to the instances when they can be fired. While this question (Would tenured professors who are charged with a crime generally be fired?) addresses this aspect for the US/Canadian system, I don't know a comparison among different systems. Edit: My question is different than US statute of Higher Education System because that question refers to the authorities and rules in different countries that grant professorships. My question is regarding the actual (technical and practical) differences between 'permanent' and 'tenured' faculty members in different systems.
I think the most important difference relates to "redundancy" in terminations. In the UK, administration can decide to stop teaching a subject at a university, and faculty may become "redundant". There are various protections in the UK such as the need to try to find alternative employment for the staff member etc. but in the final analysis, if they want to stop teaching Vedic Epistemology, the Vedic Epistemologist could end up sacked. With a tenured position in the US, that would not be sufficient grounds for termination (following university rules that I am aware of -- rules are set by each institution, though there is considerable similarity). A correlated difference is that there is a huge tenure ordeal in the US (the "up or out" rule -- either you get tenure, or you get fired), which does not exist in the UK.
Apart from the differences due to the educational systems (expectations for teaching, types of classes, recruiting grad students) and funding opportunities/expectations, one difference is that the UK system has finer gradiations of rank beyond the usual titles (Lecturer, Reader, Professor, etc.) whereas most US universities do not. This determines your pay grade and salary increases, which is fixed and not subject to negotiation like in most US universities. In terms of salary in US institutions, merit-based raises take the places of these promotions to higher pay grades, but these are much more fickle in general.