BABY badgers might have been killed after a badger sett in Ham was destroyed by the erection of a portable building, according to Richmond police.
It is not yet known whether any badgers at the site at Cassel Hospital have survived the destruction of the sett.
West London Mental Health Trust recently erected the portable building and cleared a site intended for a block of residential flats, before getting planning permission from Richmond upon Thames Council and without essential licences needed from English Nature, the police said.
A police spokesman said: "It is highly probable cubs have been buried alive and crushed to death due to tunnel collapse from the heavy machinery used.
"It is not yet known whether any of the badgers managed to survive the destruction of the sett or if they will come back to it or have permanently left the site. This has all been done with full knowledge of the presence of the sett."
Nuala O'Brien, director of communications at West London Mental Health NHS Trust said a temporary portable building was erected at the same time its application was lodged with the council, but it was "well away from a known and active badger sett".
She said: "We have badger experts on site today (Wednesday) trying to establish the facts, but to the best of our knowledge there were no other active badger setts in the immediate vicinity.
Paul Losse, of English Nature, said its role is to provide advice to the police on matters of the legislation and badgers are fully protected under the law.
Mr Losse said: "Under the Protection of Badgers Act 1992 badgers are protected from killing and injury and their setts are protected from interference and damage, disturbance or obstruction. This is important particularly at this time of year because badgers are almost in hibernation and so spend a lot of time underground."
A Richmond council spokesman said it encourages all land managers and developers to contact them in advance of any development where wildlife may be affected or threatened.