As other posters have said, this should be about where you can build the best life for yourself and your son. All the schools you have mentioned will give him and excellent start in life.
Coming from HK, perhaps you would be happier in a bigger city such as Manchester or Birmingham and by virtue of their size, they're more likely to have an expat community, if that's what is important to you.
Do you have any friend or family links or any of the cities that you have mentioned?
Regarding Nottingham, were quite happy here. We chose it 7 years ago because it's very central. It's pretty equidistant to ours friends and family, has excellent transport links so you easily get to London for example and is within short reach or several major airports.
The city itself is fairly small and experiences the same high street challenges affecting much of the UK. But it does have decent shopping and a good and improving restaurant scene.
Mapperley Park (where I live) and The Park are two nice neighbourhood in or just outside the city centre, where you will find large period houses on tree lined roads. Mapperley Park in particular is walkable to city centre and also the high school. Whilst both neighbourhoods are expensive for Nottingham, you will find them very good value compared to many other cities.
There is also West Bridgeford, south of the city which is a wonderful place it live, again, lovely homes, tree lined streets and a great small town feel just a stones throw from the city. Though it is more expensive to buy into and much less convenient for the the High School.