Yes Guy, it would appear to be a mistake/bargain, because heres the same thing in chrome at over twice the price from Halfords, although its considerably cheaper elsewhere on "the bay".
http://www.ebay.co.uk/itm/Halfords-Advanced-200-Piece-Socket-Ratchet-Spanner-Set-Hand-Tools/201221956333?rt=nc&_soffid=5024940909&_soffType=SaleEvent&_soffSubType=SALE_EVENT&_trksid=p5731.m3795Strangely the chrome 90 and 170-piece sets are also the same price as the 200-piece set youve linked (its in black, very cool, but youd probably loose them far easier!).
So, mistake, end-of-line? Who knows. Definitely daft pricing from Halfords, thats for sure. Take advantage, I say. Might even get one myself