All the major UK TV channels allow streaming online but only if you happen to be based in the UK. Try to stream from the BBC or ITV from outside the UK and you'll get blocked. The reason is that most media sites check your location by looking up the origin of your IP address when you connect to the site. This usually means that if your address is from outside the UK you'll get blocked and redirected to an international version of the site (without the ability to stream UK TV).
This video shows you how to control your IP address so that you can stream TV shows from anywhere in the world. In fact using this technique, you won't get blocked from any station in the world irrespective of your location. It's simple to use and works on a variety of different platforms, although the PC version is demonstrated in this video.