Without a backup, can I downgrade from Sierra to El Capitan? I haven't been making backups on my laptop (I know, this is something I'm going to change!) but I really want rid of Sierra, it's mucking about my wifi connectivity loads and I'm sick of it restoring Mac apps to the Dock that I just don't want there.

All the solutions I've seen so far to downgrade rely on having backups of your machine from a time where it was on El Capitan - which I don't have!

How/can I do this without having backups?
If you downloaded El Capitan Installer in Mac App Store before, you can find the application in your Purchased section on the top of the app, where you can download it again, write the installer to a usb and boot from that USB in order to install El Capitan to your Machine. Details are written here.