Current evidence is that all the episodes are extant in one form or another (16mm colour film, including stockshots; digital and tape video recordings of individual episodes). This possibly includes original 16mm negatives from which a new print of the series could be struck - if the owners of the rights and the archive material want to do that and they consider it commercially viable. Meanwhile, copies of a few episodes are known to be owned by UK collectors. A further source for recordings of the series will be the archives of foreign television companies who bought the series.
[Complete series reissued on DVD in the UK, 23 January 2017].