The issue is not the charts....the charts in current use are not the 'wrong' ones, and madamy is right about them. The charts in the UK are based on many babies whose feeding is not differentiated, though common sense suggests many of them will have been formula fed.
The 'breastfed' charts are virtually the same - apart from the fact that breastfed babies tend to gain weight faster at first but this does not show up massively. It does mean that babies who are small when young will look even smaller on the WHO charts, so using these charts to make the mothers of smaller breastfed babies better will not be successful. Yes, I do say this about once a week on mumsnet!
However, when babies get to be about 4-5 months, the charts start to look a bit different and by the time the baby is aged a year, there is a wider gap.
In the UK, there is a pilot study to test out the WHO charts in terms of their effectiveness and applicability, and in the way HVs and others use them, so we know how to introduce them nationally.
That's the right way to go about things - carefully, thoughtfully and reflectively. Any training needs that arise will be shown up by the pilot study. It is almost certain the UK will adopt the WHO charts, but it is crazy just to sub the current charts with the WHO charts without training and understanding - and it may harm babies and breastfeeding if this happened.
It's fine for informed parents and others to consult the WHO charts on an individual basis - but please, don't call for a universal change over in the red books just yet. We will get into a proper mess if this is done.