Commissario
1960, so probably still in copyright (so still fees to be paid to the authors estate), and depending on when it was last printed in a new format it potentially is a fairly major exercise to get it into an ebook format (apparently with some older books, even ones that were last published using electronic editing, it can still require a lot of manual work to get them to the point where they can be reasonably presented in ebook format - assuming the publisher with the ebook rights even has access to any computerised materials).
There can be all sorts of reasons an ebook version can be more expensive than a paperback version, including if it's had to have a lot of work to get it usable, and the expected print run, even one of the ebook champions (Baen in the states*), still can't guarantee that older books they have the rights to will get ebooks due to the costs of converting older materials suitable for paper printing, to fully electronic formats.
The book you've got in the picture, looks like it may be based off materials from the 1970's for the version that is £4, which would mean they can probably reprint that version dirt cheap (using the old print materials), but would likely have had to start almost from scratch for an ebook one
*Who have been doing ebook versions of many of their releases for over a decade.
