I'm a bit
at parent suggested list. I think of the parents I've met who've thought their dc should be G&T, and would go in and want them on a list, the dc are doing fine, but not high fliers. Otoh I suspect those whose dc are put on the teachers' list probably won't worry too much about the parents' one. Maybe it's there to warn the teachers who the pushy parents are. 
For mine, infant school doesn't have one afaik, didn't have one at the time they were meant to either because the (previous) head didn't believe in children actually doing better than others.
Juniors does have one. The top maths set is automatically, and there's a separate literacy one too. The first you know about it is when you get a letter inviting your dc to a day of G&T literacy-they have 2 a year, and invite half to each. Maths get a letter offering a very expensive lesson on a Saturday morning run by a for profit company.
Seniors is more interesting. They identify at the start of year 7 from the CATs (?) tests the top 10%. After that from exam results at the end of each year. They then offer all of them all the G&T opportunities that come up, except where it's a small number wanted. So if you're G&T in maths and you're first to get your form back for the art extra session you get it, or vica versa
. Personally I think that's a poor way of doing it.
Except for music and drama which they apoint one more person for each at the end of each year. (so there's 1 in year 8, 2 in year 9, 3 in year 10, 4 in year 11) They get quite a few opportunities to go to watch concerts etc.
Thing is that for dd1's year, the person who got the music one already plays two instuments, one in an orchestra, sings in choirs and goes to plenty of concerts etc. anyway. I can't help feeling that yes, he is G&T in music, but actually someone who doesn't already play instruments and have an interest in music firstly has no chance, and secondly probably would benefit a lot more. Not knocking this lad, just it feels to me that picking someone who hasn't already had a lot of opportunities would make more difference.