Beatrix Potter was a writer of strong contradictions. A keen business woman, the first author to license fictional characters to a range of toys and household objects still on sale today, she allowed herself to be short-changed over her royalties for years. She was an expert in natural history, boiling down animal corpses to extract their skeletons so she could understand their anatomy well enough to draw them, yet she wrote stories in which rabbits wear blue jackets and hedgehogs pinafores. A huge success, she turned her back on her literary achievements in middle age to pursue a career as a sheep-breeder.

She had a lonely home-bound childhood with parents intent on keeping her on as their companion, but she still managed to get engaged twice despite their disapproval. She lost her first fiance, Norman Warne, through his premature death and married her second, William Heelis, at 47. By then she had become as tough as the old boots she wore to sheep fairs or while working in her Lake District garden. Often seen in her oldest clothes, her resemblance to Mr McGregor, the distinctly unsmart gardener in The Tale of Peter Rabbit, was sometimes remarked on locally.

A picture by Quentin Blake for The Tale of Kitty-in-Boots. Illustration: courtesy of Frederick Warne & Co and the V&A Museum

My friend, the fantasy author Diana Wynne Jones, claimed that in 1940 her younger sister and a friend were slapped by Potter for swinging on her gate. But with respect, I doubt this. Diana’s family and mine were living in the same Quaker commune on Lake Coniston to escape the blitz. There were many cross old ladies who resented noisy young evacuees up from the south, any one of whom could easily have been mistaken by us children for Potter.

She was certainly austere, insisting on good manners from visiting children. But the number of beautifully illustrated letters she sent to appreciative readers attests to someone with a great love for the young, albeit more easily expressed at a distance.

What remains indisputable is her genius as an author-illustrator. She insisted on a miniature format for her works. This was unpopular with bookshops, which preferred uniform sizes, but was ideal for small hands. Often using a bare minimum of words on the page, she made her illustrations play an active part in taking the story forward. She was devoted to the King James Bible, always open by her bedside, and revelled in its cadences and vocabulary. “Children like a fine word occasionally”, she wrote to her publisher. Later she insisted on retaining “scuttered” to describe the hurried movements made by an evil family of rats even though neither she nor her editor could find this term in a dictionary.

Her stories have the same toughness found in fairytales, with foolishness punished and danger never far away. But her cottage interiors, with their open fireplaces, inglenooks and vernacular furniture, provide a vision of country living at its most charming.

She helped to establish the National Trust; her wish that none of her tenants living in traditional Lake District farmhouses should be allowed to build indoor lavatories or have wireless masts is offset by her generosity in leaving to the nation large tracts of countryside.

The exhibition of her illustrations in London’s Victoria and Albert Museum and the Royal Mail’s special stamp set released on what would have been her 150th birthday are testament to a remarkable author and artist. And there is still one more story to come. The Tale of Kitty-in-Boots, published on 1 September with illustrations by Quentin Blake, includes favourite characters, from the sinister fox Mr Tod to Peter Rabbit, now “older, slower and portlier”. It won’t just be children who want to get their hands on this final offering.

• Beatrix Potter’s London is at the V&A, London SW7, from Thursday. vam.ac.uk. The Royal Mail stamp set is also available from Thursday. To order The Tale of Kitty-in-Boots for £10.65 (RRP £12.99) go to bookshop.theguardian.com or call 0330 333 6846. Free UK p&p over £15, online orders only. Phone orders min p&p of £1.99.