Originally Posted by kevinofengland
I deleted them from within Calibre, I highlighted all txt files then did the search and all the newly created mobi files had gone too.
You highlighted books in the main book list window and said remove. This removes the book, all formats, and the entry for that book.
In the future if you wish to remove all text files, highlight all books and open the edit metadata window then select the format you wish to remove from the drop down remove formats window.