Hampstead Heath ponds offer a place to cool down amid the sweltering 36C heatwave engulfing the city this week.

But rule breakers have sparked fury by turning wildlife havens into their own private diving ground.

Ponds preserved for hundreds of years for their habitats and nesting ducks and swans have been invaded by impatient swimmers not wanting to pay the small fee or book online to use the mandated swimming ponds just metres away.

The culprits? All ages and genders, according to two security guards hired by the council to man the crowds of up to 50 people who swarm the pond after work when 5pm hits.

Two huge 'NO SWIMMING' signs are apparently not enough to deter the crowds of sun seekers from spoiling the nature by diving in.

The security guards stand watch all day but say they are powerless to actually catch people without the ability to hand out fines or penalties.

Now, the council has even put up barbed wire around the perimeter of the pond in a bid to physically bar people from entering the water.

A video obtained by the Mail taken on Tuesday, when temperatures reached 35C in some parts of the UK, showed around 20 people swimming into the pond and using the water pumps as floatation devices.

It follows the pond invasions that happened during the May heatwave last month, which saw crowds splash into the protected habitat while young ducklings and signets could be seen swimming desperately away nearby.

Two security guards on duty on Thursday, when the record for the hottest June day was broken once again, told the Mail they have been threatened by people when they confront them.

The officers, who wished to remain anonymous, said: 'On Tuesday there were around 30-40 people at one time in the model boating pond - how can we possibly tackle all of them? We can only question them and tell them to move on.

'They often get aggressive and try to fight us. They actually come up to us and say "we see you every day, we're watching you, trying to intimidate us".'

They added: 'We can't give out fines, we can just report it to our officer at the Hampstead Heath constabulary but the authorities know about it. But we need four or five officers to actually tackle it.

'People are still not listening, they stand here after one hour and carry on.'

'It's all ages all genders that do it, you'd be surprised. It's not just young people.'

The guards said that usually one ringleader jumps in, is applauded by others, and then tens of other groups follow.

They added that while there are good people who don't harm the wildlife, these are '10 per cent' of people, while '90 per cent' will break the rules.

But other people told the Mail they felt very differently.

One young couple called the booking system and allocation of proper swimming ponds 'bureaucracy' and said people should be free to swim in public spaces.

The woman told the Mail: 'Bureaucracy has ruined the nation - we shouldn't have to book things in advance to enjoy a public space.

'It should be a first-come, first-served basis instead of booking everything.

'I don't agree with the gendered spaces anyway too - we walked past the men's pond and there's not that many people in it.

'And apparently theirs is better which isn't fair!'

The young man added: 'Public places we are allowed to swim in are not accessible. It should be free, it should not cost anything.

'There should also be more space for people for free that you don't need to book.'

Devoted fisherman and retired artist, David Paul, 66, told the Mail he worried about the environmental effects.

'It was really bad last year I remember because people were swimming across to the little island there and you've got a shallow bank that goes a third of the way out.

'I was fishing on the platform and saw people hanging onto the pumpheads, so I would've thought that would be dangerous but they use them as floatation devices!

'It's bad for wildlife especially when they go out to there, obviously it's bad for fish as well.'

He explained: 'When they stir up the bottom it's been undisturbed for a long time there's stuff at the bottom that should not be coming to the top. Like blooms and things.

'Fishing is fine on the bottom as it doesn't disturb the birds. But last year, there was a nest destroyed which was sunk by swimmers who shoved it to the bottom.

'With the men's pond is right next door it doesn't seem necessary.'