How common is redundancy in the British (UK/Australia/NZ/Ireland) system?
Redundancies are a standard management tool in UK academia at the moment. A quick Google of the Times Higher Education Supplement suggests that there were about 1,300 academic redundancies in the UK in 2011-12, or an average of about 18 per Higher Education institution in 2011-12. At the moment a number of institutions are making compulsory cuts by closing departments. The University of Surrey is one example, as are Warwick and London Metropolitan. I'm sure there are others. The are also a lot of institutions looking for voluntary redundancies.

This all has to do with economic pressures, managerial/strategic rationalisation and either perceived student demand or disappointing internationalisation experiments.

Academic tenure, such as it was,was phased out in the UK from the mid 1970s onwards.