I'm always a little puzzled when this question arises. If you have been to university and read a science subject, the question is a no-brainer (to use common parlance): there is no similarity at all. If you read a humanity, or underwater basket weaving, then you may find the science side of the ATPL exams difficult, and wonder if they are equivalent to a science degree. They are not!
If you want to use the ATPL as a form of credit for further study, then ask your proposed course provider whether they recognise it. I can concur that the OU certainly gave it 30 points credit, as has been said earlier (so, a 1/12 of the total required), and that some aviation based MSc providers recognise it in lieu of a first degree. Similarly, the RAeS will recognise professional qualifications plus experience, in lieu of a degree for Membership status.
The CAA are not in the business, or in any way empowered, to confer a formal academic status to their exams; that is for other bodies to decide.