Start your bleeding process from the passenger rear, then move to the driver rear, then to the passenger front, then t the driver front. Always start at the furthest caliper from the master cylinder. Def sounds like air, but I'm not sure how you got that much. I've changed 100's of pads on all sorts of vehicles using your procedure (C-clamp method or disc brake pad kit) and never had to bleed the brakes after a pad install. Let us know what you find.

Better grab a fresh bottle or two of DOT4 synthetic brake fluid (recommended Castrol Synthetic or Vavoline’s DOT 4 Brake fluid). As mentioned above this may take a few pumps each caliper before you start pushing fluid. Have the engine running while bleeding. Have your buddy pump the pedal a few times, then have him hold down while you crack the bleeder. TIP, use a bottle and a tube with a small amount of DOT4 fluid in there and make sure the tube stays submerged in the fluid so, if it wants to vacuum it will pull fluid back into the system and not air. Bleed each caliper until fluid starts flowing free of air from the bleeder. Then move to the next respective caliper and begin the bled process again. You may have to go a second round depending on your results.

Pic "borrowed" from the interweb, not a Disco.

 

This is normally true for most cars, but if you look in RAVE you'll see that they recommend a different order. I'm guessing it has to do with the ABS modulator.

 

Had the same problem with my Triumph TR3 last year. turns out one of the brake cylinders had corroded the cylinder wall from accumulated moisture. Pushing the cylinder back with the new pads put the seal directly over the corroded part, and the system just sucked air when i tried to bleed it.

New cylinder fixed it. Found corrosion in the master cylinder and honed and installed new seals in that as well.

Isn't the Disco a split system? Yeah, I just looked at the RAVE. IF you have no fluid flow on either circuit, you've got a bad master cylinder, pressure reducing valve, or a problem in the ABS modulator.

I'd start by loosening the lines from the pressure reducing valve to the ABS modulator and seeing if you get any fluid flow to that point when you press the pedal.

 

Hi, Just fitted a new master cylinder and got great improvement. I can now get fluid through to all the callipers. Bled all the wheels in the order as suggested, and ran new clean fluid all the way through with no air coming out. Now I have a system full of fluid, but still no braking power at all. The pedal feels spongy but at least I have something now.
Just to add to my issues, I now have no cruise control either. Yes I took it for a spin, very scary with just the hand brake and gears to slow down.
Are the brakes and cruise Connected?
I have no visible leaks, and the fluid level isn't going down.

 

Will a vacuum leak stop the cruise control from working? With fitting a new master cylinder, what is your best guess at where?. I fitted a new O rind when fitting the cylinder.

 

The cruise control uses it's own separate vacuum pump and system The only link with the brakes is through a switch located on the pedal. If the pedal position moved when you replaced the master cylinder, that may be causing it to hit the brake switch and turn off cruise control.

If you've got pedal pressure but no brakes, then you've still got air or a leak in the system someplace.

 

Found the problem with the cruise control. My little helper whilst pumping the pedal, turned the switch off. As its always on usually, I hadn't noticed.
As for the brakes, looks like there is more bleeding to be done.