Those dates should be about right for everyone, but if you want to be 100% sure for the dates for your area, try your local county councils website - some counties have different dates by up to a week or so (though this is less likely on the summer break).
And down here on the South Coast (this thread is starting to sound like a weather forecast!!) the holidays start on 24th July and, I believe go back on or around the 3rd September.
Think steve-rob has the best idea to check on dates.