i worried about this too. but most areas in the UK do not have flouride added to the water, which most places i lived in the US, DID.
we use a toddler toothpaste for our son, but we only use a drop of toothpaste, enough to cover and clean the teeth and if there seems to be too much extra 'foam' in his mouth, i use a tissue and wipe it out! (he's too young to rise!)