Don't go all wobbly over your Webley
You can see plenty of proof that the Tempest can shoot and group OK, so yours needs a good coat of looking at to find out what is wrong with it.
It is unlikely to be anything too drastic - even though it must be very irritating for you to be embarrassed by it on the Rivvy range especially in front of IJ ( the anti-christ of of Webley pistols).
Maybe one of the resident Tempest experts could take a peek at it for you?
Rossendale Target Shooting Club. Every Tuesday and Thursday evening 7 - 10pm.