In 1922, the British Broadcasting Company was formed. Originally dealing exclusively in radio (a new and fancy technology by that point), they expanded into television in 1929. Of course, it's not like they were broadcasting Days of our Lives, they were merely playing around with the technology, getting a feel for it, with the 30 line Baird system.
Eventually, television hit the mainstream. That is right before it was all put on hold for a particularly horrific event in human history. When they came back, they were as strong as ever, broadcasting to their hearts content.
That is, until the British government got all pissy about this silly "monopoly" thing and decided that the BBC shouldn't have full control of the broadcasting industry in the United Kingdom. And so they formed the ITA in 1954. Later, the first station was launched, Associated-Rediffusion.
A-R was the first ITV licensee to go on air in the United Kingdom. They lived in harmony with all of the other ITV licensees and aired a wide variety of programming, such as:
Associated-Rediffusion went for about 9 years before rebranding themselves to Rediffusion.
This did not bode well with the ITA, who cut them from the franchise pattern for 1965. To be honest, Rediffusion had it coming. They disrespected the ITA and treated them carelessly until the ITA eventually had enough.
ITA created Thames out of old glue sticks, bubble gum, and precision welding between ABC and Rediffusion. After merging, they began broadcasting as Thames in 1968.