Question: Is there a physical layout that publishers prefer?
i.e. double line spacing in font size 12, with a 1cm page margin?
My mum once did a writing course and they told her there was a definite layout but that was years ago!
Yes. Take a look at this page...
Things may be starting to change, since there is a generation of editors now who have grown up with work processors. But publishing tends to be a conservative enterprise.
The standard manuscript format is designed to be easy to read, easy to annotate by hand, and easy to estimate word counts.
It's also pretty simple.
P.S. I based this article on North American publishing. It occurs to me that traditional paper sizes are a little different in the U.K. and you may want to check with some British publishers' websites to see what their requirements are in terms of margins, number of words per page, etc.
When in doubt, always follow the guidelines of the publisher or agent you are submitting to.