Installing a TV in a bathroom should only be done by a professional as we all know, water and electrics do not mix. You are not allowed to have a regular 3 pin socket in your bathroom only a 12v shaver port.
You will need to ensure that your telly is located somewhere where the plug can be fed through the wall and powered in another room of your house. The telly will need to be installed on a cavity wall where there is sufficient space for the telly to be sunk in to the wall. You may opt to buy a telly that has been designed to be used in a bathroom, or make a covering to go over it yourself. A 19” waterproof television may set you back about £350, so they are certainly not cheap, but the best option if you want the job done properly.
Make sure that you think carefully about the positioning of the TV as it will probably require quite a bit of work to get it installed and will not be an easy job to move it afterwards, not to mention costly. Always use a qualified electrician for electrical work and especially for any work in a bathroom or kitchen, where water and moisture can be an issue.