The normally secret Knauf plasterboard factory at Ridham Dock, Kemsley, threw open its doors to a select few when it announced it was teaming up with one of Prince Harry’s favourite charities.

Members of the Walking With The Wounded team were invited to look around the complex by managing director Ian Dean after they were picked to become the firm’s charity of the year.

The plant was built on marshland next to Kemsley’s paper mill in 1988 by its German parent company.

Bosses picked Ridham Dock because they needed their own jetty for cargo ships to dock and unload tonnes of gypsum.

Supplies are shipped from Europe.

Alternative raw material is also used which is a by-product of coal-fired power stations.

The quarter-mile long production line is claimed to be one of the fastest in Europe and has become the model for a new generation of plasterboard factories.

A second plant was added in 1993 to make gypsum and jointing products, some of which were used on the Sheppey house to be featured in an upcoming episode of Nick Knowles’s BBC show DIY SOS.

The factory gets through several truck loads of paper a day from the neighbouring DS Smith mill. A plaster slurry is sandwiched between two sheets to create a continuous board.

At the end of the line it is automatically cut into sheets, flipped over and blasted in a series of ovens to dry before being packed and shipped to building sites on a fleet of lorries.

The factory also boasts a “learning zone” run by Chris Lee. Chris and technical instructor Kevin Tarrant demonstrate how to install drywall plasterboards and other Knauf products.

Chris said: “One of the biggest innovations has been readymixed plaster which is sprayed at high pressure onto walls and ceilings Nearly anyone can use it after some basic training.

"You can do in a day what it would take a traditional plasterer to do in a week. It’s becoming very popular on building sites to tackle the acute shortage of skills in the building trade.”

Twelve of Knauf’s 200 staff at the Kemsley plant have signed up to take part in Walking With The Wounded’s Cumbrian Challenge next month through the Lake District alongside ex-service veterans who have been helped by the charity.

It was set up six years ago for former service personnel who needed jobs. But Andrew Cook, the charity’s director of fundraising, said many also needed help with mental and emotional scars.

Duncan Welston, 44, joined the Army in 1989 and spent 11 years in the Royal Engineers on tours to Northern Ireland and war-torn Bosnia. Nine years ago he was diagnosed with post-traumatic stress disorder.

He admitted: “My world fell apart. I have seen things you could never imagine but I bottled them up. I was married with a young boy but my marriage broke down and I moved into a single-bed flat.

“I started struggling with my job and two years ago I found myself homeless.”

The charity came to his rescue, gave him renewed confidence and helped him apply for new jobs. He now works in the health service selling computer software.

To support the charity, visit www.virginmoneygiving.com/fund/knaufcc