Breakfast cereals are a minefield, ingredients can only be an indication as can any published gi list
(hence you need to test yourself and portion size is crucial, 30g is the usual tested serving size)
There are 2 tests of shredded wheat on the GI index data base, neither is very low GI, one at 67 and the other at 87 (which is about where most refined cereals are)
There are several tests of All bran, none very high but they vary between 30 and 50s.
The reason for the variation is that the manyfacturers use different recipes according to country .
Special K has a tested gi of 54 in Australia, Special k in France was tested with a gi of 84
(if you look at the ingredients list they differ : sugar is 3rd on the list in France, it also contains milk powder, sugar is 4th in Australia. and seemingly no milk powder.. I assume this may account for the difference)
I haven't tried it and can't find any official tests but found a lot of people on the internet suggesting that oatibix is lower gi, it contains a fair amount of soluble and insoluble fibre and seems to be a bit lower in salt and sugar than many cereals. Tescos healthy living oat flakes have a tested gi of 50 but maybe too high in salt for you.