There is a chemical product you can get in Focus. it is in a tube in the fillers section and it is a silicone remover. It stinks like hell and wear gloves. Sorry cannot remember the make. Homebase sell it too. :)
You can buy silicone remover from screwfix. I've used it a few times, it works really well but may need a second application if the sealant to be removed is quite thick. I would avoid using too sharp a knife to remove sealant as you can nick the edge of a plastic bath/shower of even cut into the aluminium. See the removing sealant project.
Ditto, the stuff from Screwfix is fine on steel and aluminium. Good stuff, but stinks like rotten oranges???? Weird???? I might try some rotten oranges to remove silicone, you never know!
