You can now purchase the pattern from The Making Spot.
Knit toe-up with afterthought heel.
This pattern is no longer available from Mencap, as the campaign ended in December 2010.
This pattern is written to be worked on DPNs. If you wish to work using circular needles, then rather than knitting over a set number of needles of stitches, ~work each yarn to 3-8 sts before the following yarn is joined in. Then slip those 3-8 sts from left to right needle (so that the last st on the right needle is joined to the new ball of yarn). Repeat from ~ to make the main body of the sock pattern.