This article explains the different ways of watching television online,(such as I Player, 4od, Sky on demand and Youtube) and the benefits and problems with each.
TV channels' websites
The most obvious starting point for watching television online is television channels’ respective streaming sites.
As piracy was hitting its height in the mid-nineties, British TV companies (and others worldwide) were wracking their respective brains, pondering how to fight this indirect attack on their industry. BBC as pioneers
BBC were pioneers in this sense. In 2007, they introduced to the public a streaming site called I-Player on which viewers could watch and listen to all BBC TV and radio shows live, free of charge (technically, presuming one has a UK TV license, but this is done merely on faith). Unlike many other routes, it was reliable and had very high streaming quality. Benefits and drawbacks
Shows are available for a week after initial broadcast, with only sport and film affected by stringent broadcasting laws being the exception to this rule and only being available live. The TV license is undoubtedly quite costly and much-maligned but I-Player is obvious testament to the fact that this is being put to some good use. Other TV channels were quick to follow suit. Channel 4 launched 4 on demand, or 4od as it's more commonly abbreviated. Again, it is a very reliable and legal service, with shows requiring 'now download' or 'time to buffer'. The un-skippable adverts are a little irksome but remain a small price to be paid for such a service. ITV offers a similar service in ITV Player, but far fewer shows are offered for viewing. Similar services are offered by American broadcasting giants including ABC and NBC, but these are unavailable in the UK due to legality (at least barring some devious technical wizardry). Sky Television also has a similar 'On demand' service available to paying customerS, with Sky Anytime allowing mobile TV. 'TV Catch Up' is a fantastic site to watch any terrestrial or Free view channel live.
Youtube and other such video-sharing websites are also good sites for watching TV online. Short clips of segments, out-takes or classic catchphrases are legion, but shows can often be found in their constituent parts, if not in their entirety.This is increasingly common since 4od, for one, has allowed shows to be broadcast in such a segmented way.
One can also find numerous sites showing TV and particularly live sports on your PC, if somewhat less legally. Due to their underground nature though, they are often being shut down. They tend to be unreliable and plagued by slightly irksome pop-up adds.