They ask you… and in your guilty/innocence you admit it.
they then ask you to sign that you admitted it.

There has (apparently) yet to be a court case where the TV licence people presented their evidence. Magistrates (understandably) accept the word of the ‘professionals’ and your admission, however if challenged… the evidence (if they had it) seems to be too secret to reveal in court… !

The internet… would be very difficult to prove..
do they come in pairs..or only 1 witness…
they have no right to enter the property.. or even demand that you speak with them…

So even if they claimed they saw you through the window …..

Worry not.. it is an ancient piece of nonsensicle legislation that has passed its time.
TV’s are used for more than watching TV
PC’s are used for more than writing documents…and calculating sums…

Want to get a knock on the door having been asked for the address where teh PC was installed… like you do, when you buy a TV ?
why not ? you can watch TV on a PC…so surely the same rule applies ?
References :
campaign against TV licencing
http://www.tvlicensing.biz/

Telegraph campaign against TV Lic Bullies (nov 2008)
http://www.telegraph.co.uk/comment/personal-view/3563646/Time-to-stand-up-to-the-TV-licence-bullies.html

every address is on the tv license website and if you dont have a tv license the inspectors will check on the property to see if you can recieve LIVE tv pictures on your tv through the tv aeriel or from the internet,

if you DONT watch live tv on the internet or tv you wont need a tv license,

but if you do watch live tv on your pc and tv, then you will neeed a tv license and you could get fined upto £1000
References :
never paid for a tv licesnse for over 5yrs due to i didnt watch tv just watched dvd’s and ps2

and i had the tv inspectors visit my house to see if i recieved tv pictures, which i didnt, and you dont need a tv license if you dont watch live tv