Mandatory expulsion is certainly one way of dealing with plagiarism. Another way, which both academics and students may consider fairer, and therefore more appropriate, is to assess the context of proven plagiarism and to penalise in proportion to its severity.
For example, a first-year undergraduate found guilty of a single offence of plagiarism for the first time might have appropriate marks reduced (perhaps to zero) and receive a stern warning; while a second-year student found guilty of three offences of plagiarism, in the same year or in successive years, might be expelled.
Clearly, in each department there will be a range of contexts and associated proportional punishments.
But plagiarism and its management is only one of a number of contentious issues academic institutions, and in particular examination boards, deal with regularly. Others include defining what counts as extenuating circumstances, managing late work, making judgements on borderline classifications and recommending sensible mark distributions for use in assessments.
As for plagiarism, boards will need similarly to have developed a considered position on each issue. If a board has such positions, it would seem unreasonable that external examiners should then expect to have their position on an issue automatically accepted whenever there were differences with the board. It should be sufficient for external examiners to know their advice has been offered to a board for it to consider and reflect upon.
Stewart Green Senior lecturer, faculty of computer studies and mathematics, University of the West of England, Bristol