http://www.netrover.com/~timt/cheats/g/ghostngoblins.html (Amiga Plus Extra No. 5/97, 05/1997)On the high score table, enter your name as ")!(". This will make you invincible. Although, you will still lose your armour if you get hit.
The following only works on some early releases:
Type "DELBOY" on the credit screen for invincibility.