Two local divers called in to comb Hampstead Heath’s Men’s Pond recovered “rubble and construction debris” after a bather suffered a serious gash to his abdomen last week.

Precisely what caused the injury remains shrouded in mystery as the City of London Corporation (CoLC), who manage the Heath, did not specify what these objects were.

Actor Mathew Wernham underwent emergency surgery at the Royal Free Hospital after suffering the injury diving in.

The divers, who regularly assist with “clean-up dives” in the ponds, searched the pond floor on a week ago today (Thurs) as part of the investigation into Matthew’s injury.

The CoLC have since put in place additional safety measures to protect the public.

One of the divers, Paul Mylrea, told the Ham&High: “What did we find? Basically bits of rubble and construction debris, of the kind you would expect in a pond that’s more than 100 years old.

“These are wild swimming ponds, not swimming pools. The water is naturally murky. Of course you need to take care when jumping or diving into something where you can’t see the bottom. But I have no concerns about continuing to swim and dive safely.”

After the accident, Mathew tweeted warning: “Please be careful everyone!

“The water is much shallower than usual, and waiting to go into surgery at Royal Free next to a floor to ceiling photo of the ponds really isn’t the way to end a Sunday swim.”

Royce Cronin, a friend of injured swimmer witnessed the accident and tweeted: “My friend dived in from a spot marked for diving and got horrifically injured.”

The accident occurred 11 months after a new 16-foot diving board worth £10,000 was installed at the pond.A spokesperson for the City of London Corporation, who manage the Heath, said: ““On Thursday divers were sent into the men’s pond at Hampstead Heath after a man was taken to hospital on Sunday, 5 August after he dived off the jetty and emerged with an injury to his abdomen.

“Divers found several objects which have since been removed.

“The public’s safety is our number one priority. Following the incident, additional safety measures have been introduced and diving is now allowed only at a depth of 9ft.

“We have also put up additional signage to reinforce the message of safe diving.”