GdiG, I think you are right to question the relevance of the WHO statistic to UK mothers. The majority (though not all) of those 'bottle deaths' are from enteritis, basically, diarrhoea, and this comes from not just the dirty water, but from the fact that formula does not contain antibodies which protect against infection. Babies and toddlers do not die of enteritis/diarrhoea/dehydration in the UK - formula fed babies have more gastro-enteric infections than breastfed babies ( many studies confirm this) but of course they are treated quickly and efficiently when needed.
However, a study was done in the USA to see if formula feeding caused excess infant mortality in a developed country, and they found that it did.
You can find the newspaper report from the Washington Post on this study here .
I don't want anyone to be anxious about this or feel criticised - this is for information only, which was asked for. The researchers don't know all the answers, though protection against infection is certainly one, but one of the possible reasons they give for the comparative safety of being breastfed is that they think breastfed babies may be physically closer to their mothers more of the time, and are therefore less likely to have an accident. So it is certainly not direct cause and effect in all cases.
Occasionally, babies in the developed world do die directly from a contaminated batch of formula - there was a case in Bedlgium a couple of years ago, and recently, some babies in Israel died because their formula was missing a vital enzyme because of a manufacturing fault.
This is not to frighten anyone. I don't know of any contaminated batch of formula in the UK that has led to infant death or illness.