Why are there differences in formatting between the Anglia Ruskin guide and the AGPS guide (and others that you might find via Google)?
The Lund University Harvard style page provides the following explanation:
"Most reference styles are based on manuals published by scholarly associations or by publishing companies. This is not the case with Harvard, and, consequently, there are not one but several versions of Harvard style. The differences between the different versions are small and mainly concern the use of punctuation.
When guidelines within the same reference style differ, as is the case with Harvard, it is important to pay attention to consistency. This means that although the use of punctuation may differ between style manuals, writers must always be consistent within their texts."
What does this mean for you? You should ask your instructor whether they have a preference for a particular version of the Harvard style. If they do not, as Lund University suggests, pick one version and be consistent in using that version.