Wilkinsons currently have on offer Persil Comfort Naturals for half price at 98p however on the bottle there is a removable £1 off coupon. Easily remove the coupon, it is attached to the lid by a piece of tape, before or at the till and hand it in and get £1 off so if you are buying other bits you get 2p back. I picked up 2 bottles ended up getting them for free and got 4p back. You can do this its not underhand or anything because you are actually buying them so you can use the coupon.
You can use the £1 off on any Naturals range or better still use them in Tesco or Asda against anything.
If you dont feel like doing it invest 98p buy a bottle take the coupon off, go back in get the same again and use the coupon. You then get it for free and you get another coupon, you could go on and on.