Def. book lice/mite's they live in damp areas. silverfish are more pointed and elongated than the more oval rounder booklice.
They can spread to other damp area in your house if you were to cross contaminate buy taking an item from the bathroom and placing it somewhere else damp. They can breed very quickly too.
They are called book lice because usually they live in damp mouldy old books where they eat the mould that grows on the spine of the book itself. Therefore these lice/mites require damp and mould, if you take these requirements away they are more than likely die off. They can also be spotted in a kitchen under a cabinet where a kettle is boiling the steam makes the wall and under the cuboard damp which they love, soon they will be in your cuboard in your flour!
Therefore remove any mould however small, and dry the room.
To remove mould look very closely some mould is very small, spray the walls with dettol mould and mildew remover (green spray bottle sainsbury.) Try not not get on clothes or other fabrics as it contains bleech. Dispose of any old wooden furniture or old papers, cardboard which the mite love to live and breed on.
To dry the room, use a dehumidifer buy or rent one, ask if a friend has one you can borrow. Long term use or fit an extractor fan to the bathroom if you have one let it run longer. If not possible try to leave the window open as long as possible. This is all to reduce the damp = mould = lice
Also try insect sprays - be careful about pets
Also try sprinkling on talc powder, or using a hair drier on them to dry them out.