TESSA Hainsworth, cheerful, blonde and bubbly, is showing me a view of boats moored on a Cornish creek at sunrise.

"That was my drive into work," she says. "I had to keep pinching myself."

There are other photos too, which Tessa took when out on her post round in all weathers. There are the three geese which she named "the flip-flops" because of the noise their feet made, padding over to greet her.

There is a farm dog leaping up at the window of her van, eyes begging for a treat she might have in her jacket pocket. And another picture shows her post bag in the back of the van, a lettuce which was a gift from a customer slung on top of it.

She might have got very wet and tired at times, but there are clearly many compensations to being the "posh postie" in this beautiful corner of south Cornwall.

We are sitting by the harbour of the town which is called St Geraint in Up With the Larks, Tessa's engaging tale about giving up the corporate grind for a new life as a postwoman in Cornwall.

She says she'd prefer me not to reveal the true identity of St Geraint "to preserve the mystique for readers as long as possible", although many local readers, I am sure, will be able to guess.

Tessa used to struggle in by Tube and bus to her plush central London office, lightly scented with Body Shop products. She was earning good money as UK marketing manager for the ethical cosmetics company.

She had been with the company for 20 years since its exciting early days, working directly with its inspirational founder Anita Roddick. Now though, as the new millennium dawned, she was beginning to want something different.

"I was hardly seeing my children," she says.

She and her husband and son and daughter – Will and Amy in the book – moved to Cornwall with vague plans of opening a paint-your-own-pottery business.

They soon discovered, though, that this would be a non-starter in a county where incomes are low and "every second person is a potter". Tessa's husband, an actor, was struggling to find acting work.

Then Tessa heard in the local post office that the position of "relief postie" was vacant.

"I heard that the previous postie had lost two stone, and I thought 'I hate exercise, so it might be like being paid to exercise'," she says.

She got the job and set out to start out on her first morning, to learn one of the rounds she would cover, shadowing fellow postie Susie.

"That first morning, I had to get up at 4am, and the stars were still out," she says.

"I thought that being a postie was just about delivering letters through letterboxes, but there were 300 drop-off points, and it is a 60-mile drive and you are going up all these farm tracks, and everyone has quirky places where they want their post, and you have to remember them!"

She also had to remember the treats which each dog was expecting; Susie, who had done the round for 18 years, made a point of feeding them.

"There would be all these little eyes looking at me beneath gates," she recalls.

Delivering the post, she found out, was much more than delivering mail. She was a lifeline of social contact for people living in remote farms and cottages. "There was a lady who had broken her arm and said 'I can't zip up my coat and I've got to go out'," she recalls.

Another time, she babysat for a few minutes while a young mother popped to the shop for a pint of milk.

The weather doesn't get her down, although it can be pretty damp, but the imperiousness of some of the second-home owners does.

Some could, she found, be pretty snooty to the postwoman who struggled through the wind and gales to their door, and refuse to reverse even a tiny distance in their huge 4x4s to allow her past in her humble postie's van.

The anecdote about running over a second- homer's cat, and being asked to put it in the freezer for when they are next in residence, didn't happen to her, although it did happen to someone she knows.

The most rewarding moment, without doubt, in her job she says, was delivering a telegram from the Queen to a 100-year-old resident – "you have to ring up Buckingham Palace to confirm it afterwards". The strangest deliveries, meanwhile, were the anchor, sent to a St Geraint fisherman from fisherfolk relatives upcountry, and a fish, which felt disturbingly like a human limb through its packaging.

To her colleagues, she is always the "posh postie", a title which stuck ever since a customer rang in to complain that the "posh postie" was leaving her post on the mat, where her cats would use it as a litter tray.

Tessa finds out that two colleagues had a bet on her giving up the job by Christmas, and her upcountry friends were no less sceptical.

"They were saying 'the first time it rains, the first time it snows, you will give up," she says. But Tessa proved them wrong, sticking the job for three-and-a-half years, and only giving up to help her husband in his business.

"In my old job, the only me time you had was when you went to the loo," she says.

"Doing the post round, though, you are out on your own, and you have so much thinking time, it is absolutely fantastic. I used to relish those times.

"I loved it, I had never lived in the now, I was always forward planning. Being a postie, you live in the now, there was a beginning, a middle and an end to each day and when I'd delivered the last letter, I was free to be a mum which was the best thing of all."

Feel-good read though it is, Tessa's book doesn't gloss over the downsides of living in Cornwall, as opposed to just holidaying there. The scarcity of well-paid jobs means people have to take multiple part-time jobs, often with little security to make ends meet. One of the characters in the book is a farmer who can't stand holidaymakers but is forced to do bed and breakfast to make ends meet.

She is also candid about the long time it took her to feel truly accepted by the locals. People are friendly on the surface, but, she feels, rebuff her attempts to become real friends.

It takes a crisis, when Tessa's husband was rushed into hospital, to reveal how much her neighbours and colleagues care, as they rally round to pick up her children from school, cook meals and even cover her shifts.

She says the community was "so different" depending on the presence or absence of the tourists.

"It has got a buzz in the summer. It is funny, because everyone walks around with their brain disengaged and when you are trying to work, they are driving along and they have got their maps out. In the winter months, it takes on its own personality, the community spirit is a lot stronger."

She now feels very much a part of Cornwall life.

"I was walking on the beach today, and it was so quiet, there was just one other family there," she says. "I still pinch myself. Our life is so different and has slowed down so much.

"My birthday was in October and instead of going to a fancy restaurant, which we would have done, we took some wine down to the beach with a gas ring and prepared the mussels and shoved them in a pan, and had moules marinières as the sun was setting. I thought, 'This is magic'. I still love it."

Tessa Hainsworth will be signing copies of her book at W H Smith in Truro on Saturday July 4 (10am-4pm); at the Falmouth Bookseller on Saturday July 11 (from 2pm); and at The Bookshelf in Saltash on Monday July 13 (10am-1pm). Visit www.upwiththelarks.co.uk to see a clip of Tessa talking about her move to Cornwall.