There are a few.
There is FilmOn, they have to be free within the UK to comply with UK laws, and they are. The catch with them is that their free browser based service has very poor quality. That said, their free mobile based quality is comparable for the most part to TV-Catchup. I've been using them a bit and I especially like their iOS features which includes good Airplay. They do have a subscription service which provides better quality, but is quite expensive.
Zattoo is a Swiss company that does the same thing. I don't know if this works in the UK for free (I'm not in the UK), but if you have a SmartDNS service, their free service works anywhere in the world. You can record up to 6 shows from their selection of channels in the free service. The quality is not quite as good as FilmOn or TV-Catchup, certainly good enough for mobile devices, but when enlarged to full screen it is a tad worse. They have an affordable monthly subscription as well, which includes the ability to record up to 250 shows, plus access to every show for the last two weeks (basically, they record every show and keep for that time period)
AERTV is an Irish service that offers the same things for Ireland (their channels) which is free, but for a small monthly fee you also get some UK channels as well.
Of the ones mentioned above, TV-Catchup has the best video quality when free services are taken into account, it also has the most amount of UK channels. So, it is a good service.
We shouldn't forget the official sources as well. BBC, ITV and Channel4 all offer their own live feeds, and from what I can tell, all of them are better quality than any of the free services above. But Channel 4 is a bit hard to get on mobile devices until later this year.