On the high score table type one off the following:

             "R.J.TOONE"_____________For infinite lives.
             "BUMPER"______________For infinite bumpers.
             "PUSSYCAT"____________For nine extra lives.
             "BARMY CAR"_______For an extra 1000 points.
             "WOOAARRGGH"______________For faster turns.
             "WHOOPSIE"__________________To skip levels.
             "ARNIECAR"____________100,000 bonus points.

Also, if you want to stop press the 'Z' key for brakes, and to get
extra letters leave a single dot at the end of the level to make
one appear.