I think it might have changed, unless it varies regionally of course, I say that as DD is the only one being set G&T group stuff in ine of her subjects in her year, byt mot do in her other G&T subjects - so it can't be the top 10% - I did used to think it was the top 2, but since the other left the school, it's only been DD getting the extra work in one subject, so it's not that in her school either
Other than that I would agree with everything Kew has already said,
with DD she gets work set at her ability - ie: work to chalange her more, for some subjects the G&T kids are taken out & taught separately along with top set kids & then there's been the occasional special event type work, usually outside of school or outsiders coming into school to teach them something off curriculum, such as film making - though these are rare treats more than schooling IYSWIM
DDs school have always set her more challenging work through KS2, but working alongside the rest of the class, so it's not obvious - even with her being the only G&T DC for Math, but she still sits on a table with others, work is similar, just more advanced - so like I say, not at all obvious.
Maybe asking what work your DD is being given compared to the rest of her group would help - is it top set work, or work for G&T & she still works with the top set, so she's not sitting alone or in a very small group & as Kew has said, most importantly how DD feels about the work she is being set - if she's complaining its too easy, then the teachers need to address that