If you don't live within their control, they don't want you to see the propaganda they put out on their "British Broadcasting Corporation" (BBC) television stations and web site. Needless to say, there are ways around their entirely pointless technical restrictions.
(Note_To_Self: As somewhat dyslectic person, I'll never forgive patio11 for nick-naming his product "BCC").
I would like to say that by-passing government sanctioned Internet restrictions is simple and easy, but it's not true. Doing it safely can be impossible at times, and considering the rather severe punishments for getting caught (i.e. death), it may not be the smartest choice you could make. If you want to take your chances, there are often technically possible ways to by-pass the restrictions. It's not easy, and it may not be entirely safe, but usually, it is technically possible.
There are free solutions out there like Tor ("The Onion Router" https://www.torproject.org/), but they mostly suck. If you don't believe me, then just try using them. The other problem with the free solutions is a lot of government filtering knows about them and adjusts accordingly (when possible). There is also a lot of monitoring an profiling done on the traffic on the free solutions like Tor since the traffic is interesting.
If you need a solution that sucks less, you'll need to pay for it. As much as many would like to believe otherwise, bandwidth and servers are not free, so when a service is unable to support itself through advertising, then you'll need to pay for it. The commercial VPN vendors are more reliable and have far better security, privacy and performance than the free alternatives.
I've been a paying customer of https://www.tunnelr.com for over a year, and really enjoy their service. I'm on friendly terms through email with the two founders, Daniel and Jared, so I'm probably guilty of some sock puppetry or fanboyism. They also run the "devio.us" free shell provider service which is very impressive.
The thing to realize is the people responsible for controlling the network you are on and enforcing the restrictions probably have a way out of their own. It could be that their "day job" gives them access to the "other" side of their censorship filters, or possibly they've left a few holes here and there that they can use to by-pass their own filtering system. If the latter, it's probably done with a VPN of some sort.
In the case of a good commercial service like tunnelr.com, you don't need to worry too much about figuring out where things were left open.
Typically, if UDP traffic is found going to port 53, most people expect it to be DNS lookups from client systems. Again typically, if TCP traffic is going to port 53, most people expect it to be DNS lookups done by DNS servers. Of course, if you see TCP traffic going to port 80, you'd expect it to be going to a web server...
The common expectations are not "wrong" in most situations, but these expectations can be wrong if things are configured differently.
In the case of good VPN services, things are configured differently!
For example, I can use TCP and connect to port 80 but establish a SSH connection, or use UDP and connect to port 53 but establish an OpenVPN connection.
This kind of trickery will not fool filters with the capacity to do "Deep Packet Inspection" ("DPI" e.g. protocol profiling), but the vast majority of filtering tech out there can't do deep packet inspection all of the time. It requires too much computation to be effective on fully saturated links, so it slows things down terribly. There are a few products out there that can do DPI at "wire-line" speeds, but they are hellishly expensive and fairly difficult to manage properly.
BTW, if you go the SSH route, check out dsocks by Dug Song. It runs on most UNIX systems, on MacOS, and on MS-Windows through cygwin.
EDIT: I totally forgot about countless the payment options you have available in Iran (i.e. none). If that's an issue for you, contact me privately (email address is in my HN profile).