I've discovered Napisan...and sadly I raved about it to loads of people last week.
Soaked a few 'used to be' whites in a big bucket... they were so white they went that 'i'm so white I look blue' type of effect, but they were soaking for hours and hours. Did the job though! Napisan in the nappy lane in Tesco's, smallish blue and white cardboard box
Some of my white cotton clothes have yellow patches on them which I can't get out with anything - not even bleach! They are some of the older pieces in my wardrobe (eg cotton pj's) so I've started to think maybe I should just chuck them out.
There are some really nice white cotton bed linen in this online shop. Maybe I'm just sounding a bit flash, I'm certainly working up to getting some nice new bed linen myself though, downgrading our bed linen to guest bedding!!