A quick clarifaction about Outlook email accounts. Replies are sent by default using the account that recieved the email. So create
billwood@firstdriving.co.uk in cpanel and setup that account in Outlook (there is an option in cpanel to d/load config settings - but in my experience to get that to work you need to d/load the settings for outlook express and then when you next start Outlook it will pick up the outlook express settings). Do a similar thing for your other domain and all should be well
David