The Swiss Cottage branch was due to reopen at 139 Finchley Road in north-west London on October 21, inside MG Post & Wine, following its closure earlier this year.
But Post Office Ltd has now announced that the planned reopening can no longer go ahead.
A Post Office spokesperson said: “Unfortunately, due to unforeseen circumstances we are no longer able to proceed with the planned reopening of Swiss Cottage Post Office at MG Post & Wine.
“However, we are working hard to find an alternative location to re-open the branch elsewhere to restore service to the community.
“We will update customers once we have further information.”
The Swiss Cottage branch originally closed in April after WHSmith at Harben Parade, which housed the Post Office, shut down.
The new site had been set to offer services from 9am to 5.30pm, Monday to Saturday, providing the community with 51 hours of service each week.
Plans included two full-screened counters and one open-plan counter, along with improved accessibility features such as a wide automatic door, level entry, hearing loop, and a low-level counter with space for wheelchair users.
In September, the Post Office had launched a public consultation, inviting feedback on the accessibility of the new premises.
Customers were given until October 2 to share their views online, by email, or by post.
With the reopening now cancelled, the Post Office is once again seeking an alternative site in the Swiss Cottage area.
The Post Office said it would keep the public informed as soon as new plans are in place.
