Where did you get the Pan London Demand data and how is it calculated?
There's lot of data on the London Schools Atlas datastore - and if you follow the link you can find Projected Demand for School Places. There is methodology too although it's a bit too technical for me, really.
there are a lot of students attending primaries all within a mile of the Whitton TH site. There is, as we have discussed also nearby The Heathland School, which accepts 270 per year and TA which accepts 180 per year.
Twickenham Academy has the potential to attract more than it does from local primaries - the data suggested about 86 transferred from Heathfield, Chase Bridge, Nelson, Trafalgar and Bishop Perrin a year or so ago.
But where else do they go? Might they switch from single-sex schools or faith schools or other mixed schools much further away? There is some scope for it without harming existing preferences for which there is plenty of demand. From the rest of the 301 pupils:
47 went to Waldegrave
36 went to the Heathland
32 went to Orleans Park
10 went to St RR
10 went to Hampton Academy
12 went to state grammars in Kingston/Slough (just as likely to switch to a local TH as any would from private schools)
7 went to Teddington (from Trafalgar)
3 went to the Green School (from Bishop Perrin)
About 58 went elsewhere or private.
In comparison 118 went to Hampton Academy from Hampton Junior, Buckingham, Hampton Hill and Stanley (not including 10 from Heathfield). Out of 267 pupils in those schools, where else would they have gone to?
38 went to Waldegrave
23 went to Teddington
21 went to Thamesmead
12 went to Bishop Wand
6 went to Twickenham Academy
3 went to Christ's
5 went to Orleans Park
3 went to St RR
3 went to Sunbury Manor
About 35 not accounted for. Not enough in that category to fill 200 places at Turing House - more likely that it would split the intake at Hampton Academy.
Yes, Twickenham Academy is likely to be affected if Turing House took a greater proportion from Whitton, but Hampton Academy is being impacted in greater numbers anyway. Neither TA nor HA could make up that shortfall easily from Hounslow pupils, unless a big event happened like a school closing down.