Use plus gas or similar and leave to work, get hold of a proper impact socket of EXACT size (19mm doesn't sound right try an imperial 3/4'') preferably 3/4'' or 1 '' drive, a very strong and long bar (2m scaffold pole is not unknown)
Check rotation as ^^, place bar 20-30 degrees above horizontal and stand on end of bar.
If your a lardarse like me you will end up with 200lbs x 6 ft = 1200ft/lbs:wow:
and use some copperslip to stop it happening again:)