You need to choose between a compact camera and a DSLR. The compact will be more portable, the DSLR will allow you to change lenses (you can expand your collection over time) and usually will have a better sensor. It does depend on the type of photography you want to do and how much gear you're willing to lump around.
Whether you choose a compact or a DSLR, if you want to learn about photography you need something which will allow you to switch to Manual, Aperture Priority, Shutter Priority modes etc. Whilst it's fine to leave things on automatic for day to day shots, to get the best out of your camera you need to learn how to control aperture, shutter speed etc.
£100 won't get you that far with a new camera. But you could probably pick up a good bargain second hand because a lot of photographers do like to upgrade fairly regularly. Remember that megapixels aren't everything, quality of sensor matters more. So even a 10 year old DSLR could be a good purchase if it has been well looked after.
