Go to the password screen and type in:
1g0tp1nk8c1db00ts0n
Then there will be a cheats menu on the main screen.

To activate the Cheat Menu go to passwords and put in:
1GOTP1NKAC1DBOOTSON 
There is now a selectable cheats menu which you can make yourself invincible, 
max weapons, level select,
put it into pal mode and more!

Enter G0LVL & the level you want to start at as the password. Then Accept 
password, quit it, and start the game normally. (There is no O available in the 
password section ! Select a 0 [Zero] !!) Level 34 for example is the end-sequence.