Bosses at Washington Wetlands Centre were alerted after Government staff witnessed the sordid practice as they returned to their cars after work.

Patrols have now been set up to put a halt to the dogging at the site which is used by thousands of visitors each year.

The site is one of a list of dogging hot spots across the city that are posted on a website for people "keen to watch men and women having fun in the open air".

The incident came to light on Thursday after Inland Revenue workers who use the site returned to their cars at 5.30pm to find a couple having sex while a crowd watched throught the vehicle's windows.

Chris Francis, manager of the Wildfowl and Wetlands Trust, today confirmed dogging had taken place and said staff were being extra vigilant.

He said: "We were contacted by the Child Benefit Centre on Friday about a complaint from a member of staff who saw an incident in the car park at about 5.30pm on Thursday.

"One of the managers had been down to get his car and saw a group of people watching a car in which a couple were having sex.

"I briefed my staff about what happened on Monday and we are going to be monitoring the car park and passing on any suspect registration details to the police."

The secluded area, reached by a single-track road, is used as an overflow space by Government staff at Waterside Park and visitors to the Wetlands Centre.

But now it is allegedly one of the city's public dogging hot spots.

Other sites named by dogging enthusiasts include the car park near McDonald's in Ryhope, Claxheugh Rocks and behind shops on Front Road in Ford Estate.

Mr Francis, 42, said the car park, which is leased to the centre by Sunderland Council, had been used in the past by "courting couples" who leave behind "debris" after late-night rendezvous for trust staff to clear up.

He said: "A couple of years ago the car park was known to sometimes be used by courting couples and we'd have to pick up the debris afterwards to prevent a public health risk.

"But it would appear it has now become a far more serious issue as this has happened in daylight when families could have been going past to feed the ducks at our pond.

"It is very frustrating because if there's a problem with the birds or the park's cafe or school programme, for example, I can control things.

"But this is an antisocial behaviour issue which I understand is not only happening in the public car park near here but across the city".

A police spokeswoman said: "No complaints have been made to police about this matter."