easiest way (in my opinion) is goto http://www.tvguide.co.uk/ and if you look just under the channel names in the list on the left the ones that have watch underneath you can view "live" just click on the word watch.
the dictionary defines a television as : broadcasting visual images of stationary or moving objects.
Therefore i would presume that you would need a license to view tv on the net.
Laks is correct, I assumed the question was purely about live TV streams on the net. which you do need a license for regardless of if you actually own a TV receiver or not.
but if you are watching "catch up" tv and do not own any other method of receiving tv channels then you don't need a license.
But as I said the whole system at the moment is virtually unenforcible.