Hi Elaine
OK, in the site settings do you have http://sanderson-windows.co.uk set as the web address (Wrench icon → General)?
In your Publishing bookmark for the site, verify that your protocol is correct (FTP or SFTP), Verify that your server is correct (ftp.sanderson-windows.co.uk or whatever your host tells you to use and add a :PORT# if the host tells you to),
Your username and password should be good but make sure the case is observed, if you type a lowercase letter where there needs to be an uppercase then that can cause issues, same with substituting 0/O and I/1 - just be aware of this if needed otherwise ignore.
Path should be configured to what the host tells you, some use / some use /public, some use /public_html, some use public_html and there are a multitude of other site root folders for a website but the hosts support docs should tell you the entire configuration.
Once you have those things checked off, if you have no success publishing, I would give the host a shout and go through the settings with them until publishing is resolved.
Hope that helps.
Brad