The decision by Swale Borough Council related to an application for more time to carry out remedial work required as a condition of a temporary planning permission on a travellers site near the village of Hartlip in Kent.
In March, the committee turned down the application, despite a recommendation in a planning officer’s report to approve it.
Among the reasons for its refusal, according to the council, were that it would "cause demonstrable harm to the visual amenities of the area and the character and appearance of the countryside" and harm to highway safety.
However, a subsequent decision notice mistakenly stated that the application had been approved, which meant the decision became legally binding. This prompted the council to apply for the order in court, with the action led by the council leader Roger Truelove.
A council spokeswoman said: "Unfortunately, the refusal decision notice was mistakenly entered onto an approval letter template and the error was missed when being checked before sending.
"The mistake was bought to our attention by a local resident in June, and we took the necessary steps to reverse our mistake.
"To reverse the decision, we must take action against ourselves in the high court with the council leader as the figure head, as established in case law.
"This is standard practice when a planning mistake has been made."
The spokeswoman added: "Notice of decision mistakes are not unusual in local authorities, but thankfully very rare at Swale council."
The correct decision notice refusing the time extension will now be issued to the applicant, she went on to say.
The court order granting the quashing of the permission said: "On the basis that refusal of this application may well lead to a further grant of temporary planning permission for an extended period of occupation of the site, with consequent harm to the character and appearance of the area, I recommend that this application is approved."
Last month, in a separate case, the High Court extended an injunction on a gypsy encampment in an area of woodland in Surrey, ruling that the camp was a "substantial and unlawful development in open countryside".