mum As has been discussed before forecasts of school place demand is an inexact science, until someone comes up with a complicated algorithm that ties up all the factors including the relationship between OFSTED status and demand. What is clear from RPA, St RR and Turing is that give parents what they want and demand increases. In the case of Turing and RPA that really is just a place in an inclusive coed community school like Teddington or Greycourt, albeit that the team at Turing do seem to be offering something parents regard as a little bit special in terms of inspiring leadership and communicating with parents, like Maggie Bailey at Greycourt.
Were HA and TA offering that they would have been full long ago and a Turing on their doorstep meeting the need for places around its admission point would be no threat, and it's neighbours would be most concerned with the same issues we all have finding a new school on our doorstep. I agree with Lottie that it is going to take some time for them to dismantle the LST offering and fix the problems and I always agreed with your sadly not feasible suggestion that perhaps it would be better to merge them and use one building to start again. But the fact that there is space in two schools with very significant problems does not mean the demand is not there.
Of course on average Barnes parents are more likely to have the financial resources to go private but that does not extrapolate to every parent who does actually wanting to, nor every parent having the resources to, as the manifested by issues that faced Lowther parents, a school that serves an area of relative deprivation who found themselves edged out of catchment as parents in the more affluent area closer to the school were taking up places in greater numbers than ever before. That was the bit the forecasts got wrong, the latent demand amongst those who previously were deterred from applying.