Rear brake doesn't

I can't do a wheelie and I have both legs.

I'm impressed.

Is the cable stuck still?

As everyone else has said, sounds like it could be a mismatch between brake lever and caliper, or it could be shit cable outer that's either compressing too much or moving when you pull the lever.

I'd have a look at the brake lever, near the pivot - sometimes there's a little 'switch', a bit of metal or plastic that you shift in a slot to change the amount of cable pull: one position is right for V-brakes, the other is right for calipers or cantilevers. If it's there, it's most likely visible when you pull the lever back to the bars: check that it's in the same position for both back and front brakes.

Other than that, check the brake outer is decent and not too compressible, that it's seated properly at both ends, and that it's not got huge loops that move all over the place when you try to brake.

Fixed it, slightly dodgy cable route, a toed out pad n a slipped brake mounting, pissed with it n I can now lock the back brake :) cheers for the pointers

But is the cable free?

Also what the fuck is that lever^^?

Cables as free as nelson mandela, spotless n stainless
There was too tight a bend in the cable as its moved when I've been Pissing about, its all adjusted aswell as I can do n spot on now

Front feels shit now tho, might be a stiff cable ;)

Front feels shit now tho, might be a stiff cable ;)

This time it's definitely the cable inner...

Well done on fixing the rear.