I did this worked a treat
1. Reboot
2. Hold apple key + s key down after you hear the chime. (command + s on newer Macs)
3. When you get text prompt enter in these terminal commands to create a brand new admin account (hitting return after each line):
mount -uw /
rm /var/db/.AppleSetupDone
shutdown -h now
4. After rebooting you should have a brand new admin account. When you login as the new admin you can simply delete the old one and your good to go again!
Now after seeing all of this, is there a way to disable single user mode and therefore block this method of gaining access illegally?