Trudging reluctantly through the park in the drizzle on a cross-country run is an almost universally-loathed PE activity.

Now imagine doing that for nearly 2,000 miles for more than five months, carrying a backpack. That is an average of three marathons a week.

But ex-Kingston schoolgirl and former Great Britain rower Anna McNuff, 30, is made of stern stuff.

Long weeks of training, including a Christmas Day 5km run with her family, were just about enough preparation for tackling the Te Araroa trail in New Zealand this year.

Miss McNuff said: “What was silly was the decision to do it with everything on my back. I hadn’t really trained with it.

“It was all off-road. The trail I was following went for a week between towns so I would have to carry seven days of food.

“I started this being absolutely petrified, thinking, ‘I’m an idiot’.

“You get to the most incredible places. I just love exploring.”

Miss McNuff set out on the trek, from Bluff on South Island to Cape Reinga on North Island, to support Outward Bound, and has raised more than £3,000 so far.

The charity uses the outdoors to help children develop greater confidence.

The run was even more taxing than Miss McNuff’s trek around the US in 2013, during which she cycled through every state, she said.

The former Tiffin Girls’ School student added: “The [biggest] mishap was I rolled my ankle, overbalanced. I had a very difficult decision to make because I was on my own. I hadn’t seen anyone for two days.”

The solution to this blow to morale was to pull on the “magic pants” – leggings that pictured a unicorn battling a robot under a rainbow – and keep going.

She added: “I strapped it up and hobbled on. I was icing it in rivers.”