BBC news tonight explained that UK charts are based on babies including formula fed babies'. In the UK the data sets used to compile the charts have no differentiation between method of feeding - ie there are breastfeds, formula feds, mixd feds, early solids, all in the mix.
Anyone can read more info in their own red book - the provenance of the charts is explained, and I think they come from about eight data sets. Our charts (UK ones) are fairly recent - again you'll see a date in the book, and from memory it's early 90s.
The newspaper report I have seen does not make any of this clear. It is confusing the situation here with the one in the US, where charts may well be based on formula fed babies and for all I know, may be old charts, as well.
The weight difference between breastfed and formula fed babies starts at about 3-4 months, but it is only really seen after the first six months or so, and it is then that mothers can be particularly misled by ill-informed HPs and others.
I've said before, the real 'problem' with charts is that they are badly interprted (at any age) and the 'whole baby' is not looked at. It's just as bad to totally ignore a chart as it is to make it the sole factor in an assessment. It's part of a picture.