The Corporation of London has put the future of Grimshaw's 43-storey Minerva Tower into the hands of a 350-strong group of local residents.
The AJ has learnt that City planners have promised the Middlesex Lane Estate Residents' Association (MLERA) that if it continues to object to the £350 million skyscraper they will recommend refusal.
Some 70 per cent of the association's members are currently opposed to the tower - for a site on St Botolph's Street - because of fears over the effects it will have on sunlight.
In response, the Corporation has commissioned independent research into the effects of a tower on the estate, which sits on the eastern border of the Square Mile.
But even if the research proves the impact will be negligible, the MLERA will still be free to block Grimshaw's designs.
The planning department's development director, Annie Hampson, told the AJ that her department 'has always made it clear that if there is substantial objection from the residents then we will recommend refusal'.
And MLERA vice-chairman Peter Rawlinson confirmed that the planners and association had cut a deal which, he said, 'gives us a great deal of influence'.
'Nobody would want to live next to a tower this size. But at the moment we are in a very strong position to decide whether to accept it or not. Currently most are very unkeen, ' he said. 'If we were not as organised as we are then we would be ignored.'
However, Rawlinson said the association may yet change its mind: 'We are waiting to see what the sunlight research concludes before we officially decide to oppose.'
A spokeswoman for the Corporation of London attempted to backtrack, insisting that the City's planners would also take into account the views of other stakeholders.
Grimshaw's application is expected to go before the Corporation's planning committee in the week before Christmas this year.
Both Grimshaw and developer Minerva were unavailable for comment.