what you have been told is correct for Lewisham. There is however a way around it! What you need to do is contact Lewisham admissions and withdraw your original list of 6 schools. You then submit a new list of 6 schools, including Kelvin Grove as one of those schools. It doesn't need to be your first choice as as in your previous application each school will be considered. If You are not eligible for higher ranked schools than Kelvin Grove, then you would be added onto their waiting list positions (basically going back into the rank order where you are at present.
Southwark residents who wish to be added to the waiting list of a Lewisham school need to follow a similar procedure but via Southwark. Be aware that if you are holding a place at one of schools you have applied for or allocated a local school you will lose this, so this process is not recommended unless you were allocated a school not on your list and it's one you definitely don't want.
Cllr Renata Hamvas
Labour Councillor For Peckham Rye Ward
4th Thursday of each month (3rd in December), 6.30-7.30pm Nunhead Library, Gordon Rd SE15