nezzie specify a screen resolution in systemd boot.

yes you can, see https://jlk.fjfi.cvut.cz/arch/manpages/man/loader.conf.5 for all options, example there:

max

Pick the highest-numbered available mode

I have /boot/loader/loader.conf set to console-mode auto.
Pretty sure you can try settings first in the bootloader menu, type h to see all options there.

    Thanks bit I've tried all options there with little joy. Will persevere though.