@GarryP, In answer to your questions
The jaggies are both on screen and export. I have been exporting in both SVG and PDF formats and it is the same for both. I attach a Word document with all of the relevant screenshots. The jaggies appear when I am zoomed out (ie. the whole illustration on one page) and when it is zoomed in. The lines have been created using the pen tool. No brushes have been used. It seems to be only some lines and not all of them. One thing to note though is when I opened the illustration in my iPad app Designer app, it didn't seem to have the jaggies problem?!?
28.02.20 screen shots.docx