Raked out grubby grouting around bath, and cut away sealant which was showing signs of mould. Grout now replaced, and left to dry.
According to YouTube videos, applying silicone sealant requires anything from a tool-box full of special tools to, well, to just a wet forefinger. In the past I've used some plastic thingies to create a nice concave seal, but having watched a door fitter achieving an excellent finish with a wet digit, I think I'll be giving it a try.