Actually, you're not referring to the original Swedish Wallander. The Swedish Wallander series with Krister Henriksson that is shown on BBC4 is, in fact, the second time Swedish TV have made a Wallander series. The original version was made from 1995-2007 and featured an actor called Rolf Lassgard as Wallander. This version has never been shown on British TV as far as I know.
The Rolf Lassgard version were adaptations of the novels by Henning Mankell, and so it is this version that the Kenneth Branagh version is a remake of. The Krister Henriksson version (2005-2006, 2009) features all new stories (except one, which was based on a novel written by Mankell since the original Lassgard series had finished).
If you get a chance to check out the original Wallander (Lassgard), do so. I prefer Henriksson over both Lassgard and Branagh however. The Swedish TV series is superb.