Sky1 has just shown the last ep of series 4 (v. good). I've no idea when it might appear on conventional TV. I know it sickening to hear from digital viewers but I think you should seriously think of getting it or lobbying for it in your house.
First because of the lousy way sci-fi is treated by uk tv, espiecially the less popular series. I've lost count of the number of shows I get with Sky dig, even if you don't pay extra for one the packages theres loads.
Secoundly because they're going to put up the cost of installation etc soon and it'll be a lot more expensive. At the moment you can get everything installed to keep inc 1 years sub for about Â£150. If theres anyway you can afford it it's worth it!