I’m probably being monumentally thick

I have an A4 document, and I want to set it up to print at half the size

Is there a way to print my document landscape at A5 size so I can get 2 prints on one A4 sheet?

tried with various print preferences but can’t manage it

Dead simple – duplicate the page (so you have two pages in your document, each with identical content on them) then, in the print dialogue window, bottom right hand side in the ‘zoom’ funtion, ask it to print two pages per sheet (although this function may be driver-specific so the exact wording and placement of that function might be different to how I describe).

Simpler than that.
>file, print
>select printer
>properties
>finishing tab
>pages per sheet button
>select “2”

Done

When I tried that it printed the second ‘page’ blank (which is why I tried creating a second identical page)

Depends on your printer driver. Some allow it easily others, not. A workaround is to install cutePDF, print to PDF (which has loads of layout options and lets you see the output without wasting paper) then print the PDF.

Are you trying to print page 1 and page 2 adjacent on the same page, or a 1-page document twice? I think CM and MF here are at angry dolphins with each other.

If the former, CM is correct. If the latter, copying the page twice is a quick and dirty workaround (there’s probably a better way but I don’t know offhand).