Walking 435 miles in 13 days is a gruelling prospect. Imagine carrying a rowing machine every step of the way.

And imagine carrying the machine to the top of the highest mountains in Wales, England and Scotland, then using it to row the height of that mountain.

This is the brutal challenge completed by former Royal Marine Commando Matthew Disney, much of it in Cumbria.

Speaking to The Cumberland News the morning after completing his mission in Scotland, Matthew said “I’m battered and bruised. It was a hard old challenge.”

Averaging 34 miles a day, he endured everything a British summer has to offer. “I faced every element. Twenty-five-degree heat, thunder and lightning, gale-force winds up to 48 miles an hour, soaked through like a drowned rat, and bitten by midges.”

It was all in a good cause. Well, two good causes. The 35-year-old from Lancashire is raising money for The Royal Marines Charity, which helps Marines in times of need, and Rock2Recovery, which helps service people with post-traumatic stress disorder [PTSD]. Both charities also help veterans and families.

Matthew’s hands and neck were stripped of skin and his feet were blistered. Surprisingly, he said his shoulders didn’t feel too bad. Surprising because he carried the rowing machine - which weighs more than four stone - on them, switching shoulders about every 100 yards.

Matthew is carrying out a series of fundraising challenges. This was the fourth of seven. One of his first was last year when he carried the rowing machine up 10 European mountains, including Mount Etna, then rowed the height of that mountain.

“I started thinking about the three peaks: Snowdon, Scafell Pike and Ben Nevis. It seemed a bit lame to just drive to them all. So I decided to walk.”

Why carry a rowing machine? “I hate rowing. I think you should face things you hate in the same way you should face things you fear.”

Matthew covered the miles with a combination of walking and jogging, depending on the terrain. He describes climbing the mountains as a “refreshing change” from his long hours on the road.

Scafell Pike’s challenges included the wind. “The peak before Scafell, there was a 500-metre boulder field and a 25mph wind. I was pinned into a squat position by the wind. I couldn’t stand up. That drained me of energy and time.”

Highlights of the Cumbrian section included a moment of empathy in Carlisle. “I saw a runner coming towards me. I stuck my hand out. We high-fived and smiled. It was amazing to have that connection.”

The hardest was yet to come: Britain’s highest mountain. “Ben Nevis was bleak. There was torrential rain. I got soaked. And there were two river crossings.”

Did he ever consider giving up? “I’m never like that. Being in the Marines, it’s always in your head that you will succeed and persevere. I did go through a dark patch a third of the way in. There were three days in a row when I realised I wasn’t going to finish by 11pm.”

He relished the sound of drivers beeping their horns and people cheering. Some reactions were of disbelief. “People’s chins on their laps: ‘Oh my god, what have I just seen?’”

Why did he put himself through this? “There are three reasons. One; to test myself and better myself. Two; hopefully to inspire other people to set their own challenges. Even if that’s walking to the shops rather than driving.

“And three; increasing awareness of the charities. The Royal Marines Charity is opening a £2.4m support hub at the Commando Training Centre in Devon for people with PTSD and other mental health issues.

“And Rock2Recovery: I know people that have taken their lives. One lad, every time I saw him he always had a big smile on his face. To find out a couple of years ago that he’d taken his life, it was a real shock. I’m optionally putting myself through this pain. Others have to go through this or worse every day, mentally or physically.”

Matthew will announce his next challenge on his birthday: August 1. It will take place at the end of that month.

His fundraising tally now stands at more than £8,000. To donate, visit justgiving.com/fundraising/DisneyRM