Can anyone advise on the best way to keep a Westie white particularly under their mouth where they seem to get grubby. I recall reading about a herbal food suppliment that would help in a dog magazine months ago but can't remember the product it recommended.

I was advised to let dirt dry then brush off. Apply chalk because it apparently provides a barrier to dirt.
Saying that mine enjoys running in ditches and comes out as black as coal. I try not to shampoo too often but if i have to i use Asda Tea tree shampoo other than that i just shower the worst of the muck off and give him a good brush. There are Westie experts who use this site and i've had some good advice from them and i'm sure they'll be along soon with advice.
What sex, age and name is your little white friend.
Budmag.
P.S sorry don't know name of product your thinking of.

Hi buy a block of chalk from the pet shop, just rub it in and let it dry, then brush off, should be nice and white again, or you can get the loose chalk from the chemist, its called calcium carbonate and comes in a large tub costs about £5+, but this should last a long time for a pet puppy, I use a soft nailbrush to brush this into the coat, now if the staining is at the side of the mouth, just lift up the top lip of the mouth and you will find the staining will be on the bottom lip, just cut the stained fur off with the scissors, this is caused by too much acid in the saliva. I use Johnsons dry foam shampoo for my dogs, I never, ever, use ordinary shampoo, as this can cause the start of skin problems in westies.

There is also shampoo for white dogs i use this on my white GSD's they come up a treat but obviously you can't wash them to much.