Dont have experience with old webley pistols. Dó know tempests.
They're just VERY holdsensitive. They are inconsistent in the way that their poi can vary per shooting session. But I also put that down to hold sensitivity.
I can get them to shoot 1 cm edge-edge groups though at about 4.5/5m and can keep 20 shots within 1 "at 10m.
I even shot a 47 ex 50 with my 4.5 Tempest. One-handed, on official 10m pistol target