The tattoos on his leg tell their own stories. The hedgehog is there to celebrate Hugh Warwick’s obsession with the prickly little beasts that he has been studying and rescuing for 25 years.

As for his new toad tattoo, the tale behind that is a central part of the ecologist’s new book The Beauty in the Beast.

It all began when the Oxford writer let his passion for hedgehogs run away with him in his earlier book, A Prickly Affair, when he boldly declared that “the hedgehog was the most important species on the planet” and that “in its grubby little paws was held the key to the salvation of humanity”.

Of course, Mr Warwick, of Florence Park, knew he was asking for trouble making such a sweeping statement.

“For me the importance of the hedgehog comes from its ability to act as a gatekeeper to the natural world,” he declared. The gauntlet had been well and truly thrown down.

Sure enough wildlife enthusiasts from across the nation were soon taking issue with his claim. He was made well aware that there were others equally obsessed with water voles, badgers, owls to name but a few of the nation’s favourites — and the idea of a new book about Britain’s favourite creatures, and the people who love them, was born.

But as well as introducing us to fascinating, knowledgeable and often eccentric characters, Mr Warwick decided to make things really interesting by putting his leg on the line.

He would draw up a shortlist of enthusiasts and write chapters on each of them, he decided. And then at the end of the book he would reveal the one that had done most to win him over to their chosen love: not only that, he would have the winning creature tattooed above his ankle.

Unusual circumstances had already seen Mr Warwick, a father-of-two, having a tattoo of a hedgehog, at the age of 43.

The tattooing had been carried out on a stage in front of a beer-drinking crowd as part of a project called ExtInked.

He had been one of a 100 volunteers ready to display their commitments to animals and plants — becoming unofficial ambassadors — by having a permanent tattoo.

“It was meant to be my first and last one,” said Mr Warwick. But the idea of a second (and definitely final) tattoo grew as he embarked on a year of travels around the wildlife obsessives of Britain.

It proved quite a journey. He went off in pursuit of a man reinstating beavers in Scotland, an adder expert in Norfolk (who, he was warned, “didn’t like people very much”) and a dolphin researcher at work in the North Sea.

Happily, some of animal ambassadors that made it on to his shortlist came from closer to home.

The first character we are introduced to is Ivan Wright, who introduced him to joys of observing solitary bees.

Mr Warwick joined him on expeditions in Shotover Hill to find how far bees travelled in search of food.

Despite having to take early retirement from his career as a microclimatologist because of difficulties with his eyesight, Mr Wright has been able to pursue his obsession with the minute beauty of bees.

His data revealed Shotover to be a hotspot for bees and one of the best sites in the county, with 99 bee species, allowing him to argue for improved protection for Shotover.

Mr Warwick found a keen advocate for the robin in Dr Andrew Lack, of Oxford Brookes University. Although he is a biologist specialising in pollination, Dr Lack inherited his love of robins from his father, David, a former director of Oxford University’s Edward Grey Institute, who is credited with developing the science of ornithology.

“As a nation we’ve developed a fondness for robins that no other nation has, and it’s a fondness we have for no other bird,” the younger Dr Lack told him.

Some of the subjects, like Huma Pearce, who seems to enjoy nothing more than clambering on to roofs at night with a bat detector, hardly hide their eccentricity under a bushel.

“Once you start, it can be hard to switch off from bats,” she admitted. “I always warn people, it ruins your sleep and your social life, and it ages you fast — it’s as good, or bad, as a drug. The trick is to hibernate to recuperate.”

But bats did not win. Nor did foxes, despite a powerful case put by the great Oxford fox expert David MacDonald, who began work on foxes back in 1972, and went on to become Oxford University’s first professor of wildlife conservation (but then the increase in fox attacks on hedgehogs might have weakened its appeal).

No, as Mr Warwick’s new tattoo testifies, the toad won. So why was the Oxford writer seduced by the humble toad — a creature usually considered an outcast and linked to stories of portent or doom — rather than the likes of otters, dragonflies and badgers?

He scored the 15 creatures on a variety of factors, such as importance and “quality of time spent with animal”.

It turns out there was no great “toad moment” to compare with his encounters with foxes, owls, bats and dolphins.

But the toad’s “ability to change, and the cryptic beauty that lies beneath the unbecoming skin” helped swing it.

And then there was the toad’s marvellous advocate Gordon MacLellan, an environmental educator who follows a shamanic spiritual practice.

The tattoos are already a staple in Mr Warwick’s lectures to groups and schools — not so much an emblem of a midlife crisis as a reminder that the hedgehog man of Oxford, compared with some, is really quite normal.

lThe Beauty in the Beast is published by Simon & Schuster (£14.99).