Sudan 1 is illegal. Apparently it can increase the risk of cancer. So for some reason your local supermarkets have been stocking hundreds of items that contain it. A complete list of the 350 items so far (a larger list is being written up apparently) has already been released (see below).
Cancer Dye List Looks Set To Grow (BBC News On-line; Sunday 20th February 2005)
For a PDF list of what to return and not eat check here folks!