Why did I forget this series ?

I picked up a cheap DVD for this series because the cast looked good, started the 1st episode and realized I'd watched it when it was originally on TV and completely forgotten it. Well not quite completely, there were half remembered scenes but I didn't know which program they came from.
In fact I personally discovered Morven Christie in Sirens (2011) completely forgetting I'd already seen her in this.
So given that I've enjoyed the 1st episode and now remember enjoying the series originally I have to wonder if sinister forces have stolen a part of my memory. Was it something in the water, subtle mind altering commands in the TV signal or perhaps something more direct - after all can anyone remember what happened that strange weekend in March 2010 ?