It wasn't running, however the car was level and I filled it until it spilled, put the plug back in, cycled through the gears for a bit, turned it off and checked the level again, took it for a drive, then checked the level again.

I checked it again this morning when the car was cold and a little started coming out of the fill hole when I undid it. It's definitely not going to take anymore, which made me assume it had previously been overfilled.