The MHRA Style Guide Online
A Handbook for Authors and Editors • Third Edition
From Chapter 9, 'Quotations and Quotation Marks'
9.4 Long Quotations
Long quotations should be broken off by an increased space from the preceding and following lines of typescript. A long quotation should never be used in the middle of a sentence of the main text: it is unreasonable to expect the reader to carry the sense of a sentence across a quotation several lines in length.
Long quotations should not be enclosed within quotation marks. A quotation occurring within such a long quotation should be in single quotation marks; if a further quotation occurs within that, double quotation marks should be used. Foreign forms of quotation marks (see 9.2) should not be preserved unless there are special reasons for doing so.
Prose quotations should not be indented, and the first line should be indented only if the quotation consists of more than one paragraph and the first line starts a paragraph in the original. Verse quotations should follow the lineation and indentation of the original. These longer quotations should be double spaced. When printed, a long quotation may be distinguished from the main text by setting it in a smaller size, indenting it, or a combination of the two.
Long quotations should normally end with a full stop; even though the original may use other punctuation, there is no need (except for a question mark or exclamation mark) to preserve this at the end of a quotation.
Avoid interpolations indicating source that introduce square brackets into the opening lines of long quotations, e.g.:
This play [writes Dr Johnson, referring to Cymbeline] has many just sentiments, some natural dialogues, and some pleasing scenes, but they are obtained at the expense of much incongruity.
The need for any such formulation can be eliminated by some such rephrasing as the following:
Referring to Cymbeline, Dr Johnson writes:
This play has many just sentiments, some natural dialogues, and some pleasing scenes.
A reference in parentheses after a long quotation should always be placed outside the closing full stop, and without a full stop of its own (see the first example in 9.5).