After starting the game (or during the game), quickly type "KAREN BROADHURST" or "KARENBROADHURST" for invulnerability. The message 'cheat mode on' should appear if done correctly. Holes and time running out will still kill you.
When the credits appear, type "DELBOY". "Cheat mode activated" will appear, and you are invincible, providing he doesn't fall down a pit.