Article 129(1) of the ANO defines a personal flying log book as something that it is not necessarily a book at all:
‘Log book’ in the case of ... [a] personal flying log book, includes a record kept either in a book, or by any other means approved by the CAA in the particular case;
Depending on what you take "include" to mean, this inclusive definition might not proscribe any form of log book at all. It simply states that two acceptable implementations are (i) books and (ii) CAA-approved means.