We don't have tenure as such in the UK (it was abolished by Thatcher). We do have jobs with permanent contracts; these used to be really quite secure (occasional department-closure redundancies notwithstanding) but the current batch of senior managers seem keen to make everyone afraid for their jobs. My own university (Liverpool) attempted more than 50 redundancies on the basis of dodgy performance metrics last year and generated six months worth of industrial action. There are also (increasing) numbers of teaching and research staff on casual and temporary contracts. Some of these are postdocs, others equivalent to US adjuncts or Visiting Assistant Professors.
Our middle and senior management are increasingly a separate class. It used to be that management was done by established academics on a temporary basis: the department's full professors take their turn as head of department, for example, and the Pro-Vice-Chancellors (deputy Presidents) would have recently been senior profs. Nowadays, heads of department tend to be externally recruited as such, there's an increasing group of senior management that have never been academics, and those that have been are essentially part of a separate management track that doesn't really interact with the career paths of the rest of us.
The traditional governance measures have also broken down: it used to be that the faculty Senate was (probably over-)powerful; now management is corporate-style in the hands of Vice Chancellors-as-CEOs with their senior management colleagues and carefully selected 'independent' non-execs serving as oversight.