Thanks everyone for replying back and sharing your useful tips. As advised, I have checked all the 3 grammar school websites (Sutton) and Tiffins and this is what I have found:
Wilsons - don't care about postcodes.
Wallington and Sutton - they have provided a list of postcodes and the common ones are SM1-SM7, KT4 and few with CR.
Tiffins - 10 KM distance from school is inner priority order.
About the tests:
Wallington, Sutton, Wilsons - share the common SET test.
Wallington - No second round, only SET! Does that mean it is easier to get into ?
Sutton & Wilsons - Common second round but different criteria.
Tiffins - 2 rounds.
First round for all tests is multiple choice - in English and Maths.
Second round is written test in English and Maths.
I didn't know they take actual mock tests at school too, so definitely would register for those mock tests and also for the open evenings in June and Sept.
I have a silly question :) I am considering moving closer to these schools - to a place which will make us in priority order for Sutton grammars plus still keep us 10KM within Tiffin. But since some of you mentioned that boys travel from Epsom/Ewell etc easily, but their post code is KT17-KT19, and thus, they are outside the priority order.
My question is, out of the 130 seats these schools offer, how many (average) statistically have gone outside the priority order ?
Since we are considering moving, I am not thinking of Epsom/Ewell but should we ?