The Prince of Wales wore his eco-credentials around his neck in the form of a recycled plastic tie, as he championed “innovators, entrepreneurs and optimists” saving the planet.

William praised the “incredible minds” working on “climate solutions” when he joined Microsoft co-founder Bill Gates at a London eco-summit hosted by the tech entrepreneur’s Breakthrough Energy organisation.

William looked dapper in a dark suit as he toured the stands of start-ups showcasing innovative solutions to help tackle climate change, and he told one firm working to limit textile waste from the fashion industry about his tie.

He was sporting a £39 royal green tie, handmade by a company called Wilmok in Italy from recycled polyethylene terephthalate, known as rPET, from plastics found in food and drink packaging.

William spent the day highlighting his Earthshot Prize, an environmental award showcasing and scaling-up ideas to “repair” the planet, to mark Climate Change Week London.

When he met fashion designer Stella McCartney, a supporter of his prize, at an earlier event celebrating the awards’ finalists, it appears the prince told her about his tie as she laughed and him it was “fantastic”.

The prince told Mr Gates and hundreds of delegates at the summit in Wapping, east London: “For me a big part of this week is about celebration.

“Celebrating the incredible minds that are working all around the world, night and day, on climate solutions, celebrating the individuals and organisations who are supporting them, and celebrating the progress we have already made.”

William chatted to Peter Majeranowski co-founder of Earthshot finalist Circ, which has developed a process of recycling polycotton, a plastic and cotton fabric, into its constituent parts and producing a new textile.

When he handled a dress made from the product William said “It’s silk almost”, and Mr Majeranowski made the prince an offer: “We’re happy to make you lots of ties if you like?”

The prince replied “(I’m) wearing a recycled plastic tie today.”

William met Stella McCartney at the Sky Garden in central London, where Ted Lasso actress Hannah Waddingham moderated a “fireside chat” with him, Earthshot Prize chief executive Hannah Jones and one of the prize’s trustees, Tokunboh Ishmael.

Ms Waddingham asked the prince for his message to the Earthshot Prize finalists, and environmental investors and philanthropists.

“Be bold, be brave, be creative,” he said.