You have to become an uploader, which requires you to contact them. The reason being firstly, they verify your uploads to build an element of trust etc, secondly they dont want people on slow connections, or who arnt going to upload for long enough to gain more seeds, and thirdly, they have some rules of what can and can't be uploaded.
For example, you cant upload stuff that will be released on DVD within 42 days or has been released on DVD, except in cases where they have acquired special permission, there are certain "high profile" shows that can't go up without special permission because otherwise it causes problems for the management (like the recent Doctor Who series, the BBC gave them permission to upload each episode for 7 days after broadcast).
Also, everything has to be UK programming, they dont want and wont allow the latest episode of Lost or 24 for instance.
Basically, the rules they have, help keep the service running as good as does, and the TV companies dont mind them running the service, the BBC has even endorsed it on multiple occasions, and used it as examples in press conferences etc of how p2p can help deliver iPlayer content.
They also have a very tight nit community on there, and dont tolerate crappy uploads etc.
The other main thing is, they are 99% of the time looking for people who can cap programs rather then just download them off another site and upload them on UK Nova.
They have a very strict "respect" rule, whereby they respect other sites rights not to have the content re-distributed etc...
Its all politics, but all I use it for is downloading and its out of this world for that haha!