Park users have been jaywalking across a busy road in Rosehill after a pedestrian crossing was installed 20 metres from a connecting footpath.
Transport for London (TfL) engineers pressed ahead with the scheme in Reigate Avenue, even though the pathway moved when new flats were built nearby.
Local people claim a public consultation would have averted the crossing chaos.
They are now campaigning for the “impractical” facilities to be realigned.
Resident Judy Murphy said: “We are very angry because the likelihood is that they will be ignored by local residents.
“This may result in people, especially children, simply taking the shortest means of crossing this busy road elsewhere, putting themselves at risk of an accident.
“We are astonished and disappointed with TfL for going ahead with installing the crossing in clearly the wrong place.
Councillor Dave Callaghan added: “This is yet another example of TfL failing to consult local residents and councillors.
"We could have told them the crossing was in the wrong place, but they refuse to talk to us.”
TfL acknowledged the scheme design, which passed a safety audit, was based on preparatory works done by Sutton Council several years ago.
A spokeswoman added: “Since then, separate works by the council moved the location of the footway a small distance farther along the road.
“Because the preparatory works had already been complete, and there was no desire to further disrupt road users by digging up the road again, the decision was taken to keep the original scheme design.”
Sutton Council said its officers would have advised TfL about the siting of the footpath had they been told about installation work.
A spokesman added: “However, we do appreciate the costs involved with moving the crossing may have been a factor for TfL.”