I managed to sort the problem by adding this CSS to the bottom of my main-styles.css file
p {
display: block;
margin-block-start: 1em;
margin-block-end: 1em;
margin-inline-start: 0px;
margin-inline-end: 0px;
}
It also fixed all the issues with the images that I mentioned above and the line breaks that were not appearing on the front end.
The WordPress editor and the front all marry up now.
Thanks