So the brakes have been progressively getting worse and I had noticed the fluid had been getting low. The master cylinder was on it's way out so I thought this was the problem so I replaced it. Installed it on the weekend and bled the system and the rear slave cylinder started leaking. So today I buy another. They only came as a pair. So tonight I put the new one in and proceed to bleed the system and get all the air out. Only to find that the peddle goes to the floor. If u pump it it gets hard and stays hard. But drive a bit and it goes to the floor again. What could this be?

Air in the system or brake adjustment
2 of the 15 likely causes of the symptoms you describe

Yep Air in the system, a fluid leak or it could be siezed rear brake pad adjuster/s
EDIT: assuming you have adjusted the rear brakes.

back the h-brake right off and adjust the shoes. Then adjust the h-brake again. Then bleed the brakes thoroughly, that should sort it..