Though it's not essential to do so, (see the link below in the next paragraph), you can make an official claim to copyright, for a small fee. The official UK website for this is: http://www.copyright.co.uk/index.html?utm_source=AdWords&utm_medium=PPC&utm_term=copyright&utm_content=147565083570&utm_campaign=AdGroup&Network=Search&SiteTarget=&gclid=EAIaIQobChMIlKDTgceP2gIVxp0bCh28WgYbEAAYAiAAEgI7XvD_BwE:
Here is a US government site that explains how to apply for copyright and makes the point that copyright applies even if it's not claimed officially, as soon as a piece of writing, design or art is put into a tangible form (a book, a film, a digital work or an object).
If someone wants to use extracts from your writing they should always write to you for permission. If your work is reproduced without your permission, you are entitled to bring a civil action and sue them for damages. (This is a civil offence, not a criminal one.)
By the same token, if you want to quote extensively from a previously published work, you need to find out who owns the rights to the work and write for permission to do so. If a writer died more than 70 years ago, the copyright on their work has expired. In the case of poems published posthumously, copyright expires 70 years after the work was first published.
If you do submit a manuscript that includes excerpts from other works, you must ensure that you have received the necessary permissions to include them.
Below are links to some of the articles that we found on the subject, for you to browse. These are not definitive answers to questions; some may conflict with others, and they are just starting points for further research, rather than endorsements or advice.