MaizieD
I have used this stuff from 'Must Have Ideas'. I know it works, though, despite its advertising, the mould does come back, but after a long time.
Website says it's out of stock ATM. If you google 'mould magic' there seem to be a few similar products available which are probably worth a try.
musthaveideas.co.uk/products/mould-magic
Yes.I’ve used that, too. My partners shower was covered in black mould and it cleared it even on the sealant. I did, however, find a similar product in a local hardware shop but not sure if it works as well as I haven’t needed it. As long as the product has bleach in a gel base so that it sticks to the grout it should do its job.