On the title screen, after the music has started, you can enter the following:

"i Use an Electric Shaver" : Collision detection ON/OFF
"Witch Ducking"            : Stops water
"Superman"                 : Super high bounce jumps
"Lazy Bastard"             : Level select
(First go to Options menu and change SELECT from AUTO to MANUAL)
"More Beans Vicar"         : ?

The screen should briefly flash to confirm each cheat entry.

Note: The cheats also "work" with the demo version - i.e. the screen flashes when you enter one of the cheats. However, neither in the demo nor in the full version could any of the advertised functions be verified. For example, the level select - this works once you set the corresponding function to "AUTO" in the menu - with or without the cheat, only the last 3 levels are selectable (counting from the ones you have already completed). The collision detection and water could not be tested since no "liquids" or enemies or other "dangerous" things were encountered - and higher jumps were not noticed either.