I've heard it's OK (always seems to be doing reasonably).
Thing about round here - traditionally, children went to the state primaries then off to private secondary (or grammar if they got in - but as you know, fiendishly difficult to get in, even if you are v bright). Great private secondaries here - Hampton, Eleanor Holles for example (and others further afield) - lovely reputations, great grounds - still (I think) biggest intake of pupils from state schools rather than private etc. etc.
However, I think (and this is my own opinion!) that in the last 5-10 years, things have changed somewhat. Because of the massive increase in house prices, those that have moved into this area (without a long history of house buying) have silly size mortgages (like us) and are beginning to realise that they may not be able to afford private school. Hence, more children are going to the local state secondaries with parents who want to be involved in their education and hey presto, the standard is improving.
My theory doesn't apply to everyone (especially those minted from the city!) but we have noticed this amongst our friends who have started to say, no matter what, our children will be going to state secondary because we have no choice.
Similarly, the council seems to have taken an interest in the secondaries (as you know, has always had a good reputation for primary), and the government has pledged money to improve them (and this seems to have filtered down to the schools - Teddington, for example, is about to be rebuilt).
I'm hoping (fingers crossed) that this trend will continue!