Thanks for the response, I should explain the reason for backup is incase this machine is infected etc in the future, I don't expect the hard drive to fail any time soon since I bought it a month ago.
Your hard drive is as likely to fail in the next 60 seconds as it is to fail in any random 60 second period in the next X number of years. The correlation with age is not very strong. If anything, the tendency is to fail early in life or after 5 years or so---along what is called a "bathtub curve".
I just want to be able to re-image from a previous back up if anything goes wrong.
Terminology:
I assume you mean "restore an image" when you say "re-image". By itself, I would take the term "image" to mean "making an image", not "restoring an image".
Do I still need to do the recovery CD in this case?
If you want to restore an image, you need to be able to boot your PC and access the Macrium interface.
How do you propose to boot a PC when your hard drive drops dead? You need a boot method. What's your boot method if your hard drive is dead?
For example let's say I get infected with a trojan and want to re-image from last weeks backup - would I need to put the drive with the backup file on it AND put the CD in to recover or does it only require the backup file?
I'm not sure I understand that sentence. You need to be able to boot the PC, access Macrium, and access the previously made image file.
You would need to be able to do this:
If the boot hard drive is still bootable: boot from it, start Macrium, navigate in it's interface to your previously made image file. Direct Macrium to restore that image file to the infected drive. (Assuming the image file is not infected.)
If the boot hard drive is not bootable: boot from your recovery medium, navigate in it's interface to your previously made image file. Direct Macrium to restore that image file to the infected drive or it's replacement. (Assuming the image file is not infected.)
If the hard drive is still bootable, but you don't want to boot from an infected drive, then act as if it's dead and boot from the recovery medium as stated in the previous paragraph.