A Gravesham Council officer has been accused of going beyond his powers in granting planning permission for the Heritage Quarter redevelopment.
Civic group Urban Gravesham claims service manager Clive Gilbert overreached in rubber-stamping the £120 million scheme in April.
The allegation comes in papers submitted by the group to the High Court, which have now been revealed.
They are part of a judicial review challenging the legitimacy of the council’s decision.
Urban Gravesham claims there was a "legitimate expectation" Mr Gilbert would send the plans back to the council’s regulatory board to make a final deliberation.
The group claims there should have been another opportunity to review the scheme after the council agreed £6.6 million of extra funding for infrastructure with developers Edinburgh House.
Urban Gravesham says this is less than three quarters of what the council was aiming for but the authority denies this.
Over the next four weeks a judge will rule the claims have merit.
If so, the scheduled autumn start date for the scheme could be put back by six months as the decision will be sent back to the regulatory board.
A council spokesman said the authority was "satisfied, having taken legal advice, that the process adopted was correct."