Anyone know where?

I worked out that microsoft charge 0.0085 pence per point... so 2100 works out at £17.85

and 4200 works out at £35.70

I've seen 4200 for £32.99 on Play.com (0.0079 per point)
and 2100 for £16.99 also at play.com (0.0080 per point)

but i was wondering if anyone had seen them cheaper anywhere else? or am i being pedantic?

Think places like amzon/play are going to the best, the points are basically MS's own currency so you won't find any half price deals or anything else like that. If you can get a couple of £ of RRP then it's a good deal.

You could always risk Ebay there might be some floating around, but as above I doubt retailers have much margin to play with on them.

the 2100 cards are slightly cheaper at shopto.net @ £16.63

http://hotukdeals.com/item/326401/xbl-2-100-points-card-15-21-at-amaz/

2100 for £15.21