Push brakes to the floor before stopping..happens about 50% of the time. Cause? on 1999 Land Rover Range Rover

Sometime when I push on the brakes the pedal stops at midway...other times I have to push it almost to the floor. When the pedal stops midway the longer I have my foot on the pedal it will eventually go all the way to the floor. Cause and cure?

Asked by for the 1999 Land Rover Range Rover
The problem was diagnosed as the master cylinder needing to be replaced! Not an inexpensive replacement! : (