‘The Pop Up Flash is quite weak (power) and because the lighting in a pub is typically around EV6~9,
the flash may not have enough power for a correct exposure as the KEY LIGHT. . . . Although I have not used an EOS 100,
I do know that typically for EOS DSLR's “Intelligent Automatic Mode” and "FULL AUTO MODE" when shooting in medium to low light level and when the Pop Up Flash is not powerful enough to act as the KEY LIGHT, then the camera’s functionality will tend to use the flash as a FILL LIGHT and reduce the SHUTTER SPEED to increase the Ambient Exposure. This is something that I expect you won't want, because at a pub I guess the group will not be playing 'statues', so, if the flash is not powerful enough to adequately freeze SUBJECT MOTION the ability to make a Faster Shutter speed is more useful than being stuck with a slower Shutter Speed.