My favorite British, Sci-Fi TV show right now is Doctor Who.
Originally premiering in 1963, Doctor Who follows the story of a 900+ year old Time Lord from the planet Gallifrey who travels the universe in a Blue Police Box called a TARDIS (Time And Relative Dimension In Space). Ok, I know that's a lot of info, so I'll break it down. The Time Lords were a race of aliens that possessed a binary vascular system (they have 2 hearts) and an impeccable knowledge of history. In the great Time War with the Dalek Race (a genetically engineered race whose prime directive is to "EXTERMINATE!" all races that are not Dalek), the Time Lords were destroyed, all except the Doctor. How he escaped and ended the Time War are still fairly unclear, although it is mentioned that the Time War is Time Locked, so not even he can go back and change things. He is a lonely wanderer destined to travel time and space (did I mention that the TARDIS is a time machine and a spaceship?)
The Show went off the air in the 1980s but was restarted in 2005 starring Christopher Eccleston and Billie Piper as the 9th Doctor and Rose Tyler, respectively. Eccleston regenerated at the end of Season 1 and was replaced by David Tennant who held the role until 2009. He went through 3 seasons, 3 companions, and several Doctor Who specials before he regenerated into the 11th Doctor, Matt Smith.
The Doctor typically has a young, human female companion that travels with him. The companion helps keep the Doctor sane since when he spends too much time alone, he begins to lose some of his finer qualities, especially compassion. The only problem with the companions is that they are destined to part ways with the Doctor eventually. Some of them, like Sarah Jane Smith and Martha Jones, do manage to reunite temporarily with the Doctor, but usually, once they are gone, they stay gone.
In addition to their unusual biology, Time Lords don't exactly "die" in the simplest form of the word. Instead, they regenerate. What does this mean? This means that the current Doctor "dies" and a new Doctor steps into his shoes. Literally. What this means for the show is new actors can take over the role with each regeneration., The current season features the 11th incarnation of the Doctor as portrayed by Matt Smith. However, the Doctor is at his most vulnerable during his regeneration cycle.
The Doctor's favorite tool and most handy device is his Sonic Screwdriver. The 5th doctor is the only one to not use it (he preferred the MacGyver method of saving the universe). the Sonic Screwdriver is very good at opening or locking doors (unless they are made of wood), but it can also boost radio signals, fix wiring connections, or shut down entertainment systems. The Doctors in the new series are never seen without it, and each screwdriver is unique to each Doctor (he gets a new one post-regeneration)
There is a great deal of debate as to who the best incarnation of the Doctor is. I have yet to watch the original series, so I have to reserve my official, overall judgement until then, but based solely on the New Series alone, my favorite Doctor is David Tennant hands down. I really liked Eccleston, especially toward the end of Season 1 when he really began to regain his pacifism and compassion that I always associate with the Doctor, and Matt Smith has a definite absent-minded, odd, not-quite-human quality about him that makes him a perfect Doctor, but I just simply love the 10th Doctor. Part of it is the way he speaks: clever, witty, a bit cheeky, and very thoughtful. Tennant's Doctor is one that I just trust innately and believe without a shadow of a doubt that he will be able to fix everything and save the world.
One of the best things about the series is all of the different types of lifeforms and aliens we get to see. From Sontarens to Daleks to Cybermen to Sycorax to Atraxi to Weeping Angels to Jagrafess to Adipose to Vashta Nerada, every episode has a new adventure and/or a new species to discover. Some of them are benign while others are deadly and will stop at nothing to defeat the Doctor or destroy the world. Some give me nightmares while others I'd actually like to meet.
At this point, it's difficult to go any further without disclosing major "Spoilers" as Professor River Song would say. So I will leave you with a quote from the Doctor: "People assume that time is a strict progression of cause-to-effect but actually from a non-linear, non-subjective viewpoint, it's more like a big ball of wibbly-wobbly, timey-wimey stuff."
"I'm running out of time/ I need a doctor..."