Pedantic remark: the paragraph as stated is false. The Defamation Act 1952 (http://www.uk-legislation.hmso.gov.uk/RevisedStatutes/Acts/ukpga/1952/cukpga_19520066_en_1) modifies the way in which some of the defences below operate. That's all. It doesn't contain defences and not all the defences listed are in the Act.

This isn't a big deal, it just suggests that whoever wrote this summary was not a specialist in the field (maybe they were working from a summary of some kind). I'd advise treating this whole summary with due caution as a rather sloppy explanation of the law.