Replace pivot screw and lock screw. Place sear spring in hole on top of sear and place it in housing and replace its pin. Then put trigger spring into trigger and push that into housing and replace its pin. Then replace the trigger stop pin. Replace the trigger guard and its two pins. If you have removed them, youcan now fit the trigger adjuster and lock screw. Replace barrel catch spring,plunger and barrel catch and replace its screw. Refit sight and grips.
Webley premier sears can wear and the gun wont cock. Thats part of the reason I suggested deburring triggr housing and stoning sides of trigger and sear. The burrs can stop the sear from moving freely and stops the sear from engaging with the piston. I used gn paste on the sear and trigger but WARNING--THIS STUFF IS SLIPPY AND I HAVE HAD GUNS THAT THE TRIGGER HAS GONE TOO LIGHT ON AND HAD TO CLEAN IT OFF AND USE MACHINE OIL. ---USEFUL TIP ON OLD GUNS!