What is the difference between permanent faculty positions in the UK and tenured faculty positions in the US/Canada?
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.