The rate of nature decline is “very scary”, a conservation scientist has warned as green groups prepare to unite for a major protest in London.

More than 350 charities, businesses and direct action groups are set to take part in the Restore Nature Now march on Saturday, with more than 50,000 people predicted to attend, according to organisers.

A host of celebrities including Dame Judi Dench and Dame Emma Thompson have urged all nature lovers to join the action, which aims to send a message to politicians to prioritise nature and climate in the General Election campaign and the next parliament.

Charlie Gardner, an associate senior lecturer at the Durrell Institute of Conservation and Ecology, said: “Nature has been in decline all around the world incessantly for decades.

“This is happening in real time – real, visible changes in the natural world around me and it’s devastating.

“It’s also very scary. I live in fear of what the future is going to be like.”

Mr Gardner, who is joining the march with Extinction Rebellion, said he also feels “a sense of betrayal” from politicians.

“As a scientist, I feel we’ve done our job. We’ve upheld our parts of the bargain,” he said.

“We’ve been out there collecting data, we collected all this evidence that makes it clear we need to change and we presented that evidence to governments, and we’ve used all the appropriate channels to try and make it clear how important it is and how urgent this shift is.

“But governments simply are not listening because they’re listening to the industries that are lobbying against nature protection laws.

“So people are taking to the streets because we’ve tried everything else.”

Craig Bennett, chief executive of The Wildlife Trusts who will also be attending the march, said: “This is the most important general election of my lifetime because the scientists have been very clear with us now.

“Whether we’re talking about the nature crises or the climate crisis, our chance to turn things around has to be this decade.

“So what that means is we need to send a very loud, very clear, unambiguous message to all politicians across the political spectrum that the great British public are nature lovers, that we’re sick and tired of politicians… treating nature as an optional extra.

“We need to give all politicians across the spectrum a massive wake-up call tomorrow and say just the public is way ahead of you on these issues and you need to catch up.”

The organisers said the march could be the biggest public demonstration ever for nature and the largest in the run-up to the General Election on July 4.

Protesters will meet at Park Lane at noon before walking down Piccadilly towards Trafalgar Square, then heading down Whitehall to Parliament Square.

Broadcaster and naturalist Chris Packham told the PA news agency that this is the first time organisations across the entire spectrum of campaigning and conservation have united, from the National Trust to Just Stop Oil.

He said: “They both have a role to play, you don’t have to like either of them but what you have to do is recognise that whilst they may not be in the same team, they’re playing the same game.

“When we pull it off tomorrow, one of the greatest successes will be having direct action groups standing alongside long established and quite conservative groups with small NGOs,” he said.

“And I think that this is testament to the fact that everyone is recognising that now is the time to accept our commonality … because we are in a last stand for nature.”

Richard Benwell, chief executive of Wildlife & Countryside Link who is also joining the march, said: “The state of nature is something that brings a lot of us fear and worry about the future.

“But this strength and devotion of people’s response to that crisis is something that fills me with optimism and hope.

“It’s absolutely amazing to see how willing people are to take the time, to put money, to put their passion into showing that we can make a difference together.”