Regarding the level of preparation required, I am astounded to see some responses above. Unless these parents are aiming at schools ranked much outside 50 or even outside 100, there are a lot of lies there, for whatever reason. In our prep and among my friends, there are plenty of parents who are okay with their DC going to a senior school ranked much lower than 50, oven outside 100, and the preparation of their children is really quite low, like above.
But if you aim at the top schools, like Hampton, LU, Highgate (or equivalent for girls' schools), it is simply not reality. If you are talking about Westminster, St Paul, Kings, SPGS, G& L etc, the extent of preparation by many parents is then at really another level.
Whatever the motive, for all prospective 11+ next year or beyond, please take note of what I said above. You do whatever preparation required according to the level of schools you are targeting.