In-game pause with 'F9' then hold 'LEFT SHIFT' and press 'F9' to unpause and you will find that the collision detection has been turned off.
Press 'F9' to pause the game and then press all the lettered keys at the same time. The game will restart and you will be invincible and have infinite time.
Pause the game, and press 'CAPS LOCK', then 'CTRL', then 'SHIFT', restart the game, with infinite lives and no collision detection.
Type "NO HUNS AT HAMPDEN AND NO SKOL AT IBROX", then press keys '0' - '9' to select that level.