I have read the Gill Rapley book so think I know the answer but just wanted to check this out with others......
My DS is 4 months old. We went to a 'weaning workshop' yesterday run by the HVs at our local clinic. They talked a lot about purees and made some up for us to taste - all fine. They then showed a short DVD about BLW. It was quite clear they didn't approve of the BLW approach - saying stuff like 'we can't tell you not to do it', 'go ahead if you want to make life more difficult for yourselves' and 'it's a new fad' 
They then said that obviously you can't do just BLW from 6 months and must give puree as well, as not enough food will go in with BLW so your baby will not get enough nourishment, - so if you do BLW you will be making your life v hard as you will still be pureeing anyway!
Myself and another mum did question this and both said this contradicted our understanding of BLW from reading the Gill Rapley book - to which the HV said she had just been on a training course run by the paediatric nutritionists at our local hospital and this was what the trainers had said - 'but go ahead and ignore the experts if you want as its your choice and you can choose to take the risk!'
We then asked if this was the official NHS line on BLW - that you must mixed feed with purée or else your child will be under nourished - and we were told yes, this is the official NHS viewpoint.
Now I've written this all out I'm starting to wonder if I should complain about this HV - but to start with, I am right aren't I? There is no need for me to make sure DS is topped up with purée....? The first stage is just about experiencing food and if some goes in that's a bonus, right?