To many prospective nannies, this advertisement on an agency website reads like a dream: a flat in Notting Hill, a car and trips to St Tropez to look after two small children, for a tax-free salary of almost £30,000. But as the world's financial markets lurch from one crisis to the next, jobs such as these may turn out to be just that.

With thousands of bankers facing redundancy, nannies are becoming a luxury they can no longer afford. Even those City high-rollers still in employment are tightening their belts and seeking cheaper childcare options, such as nurseries, nanny-shares or even leaning on grandparents, to withstand the next financial earthquake.

For more than a year, Katie worked as a live-in nanny for an American family in a large house off Sloane Square in Chelsea, West London. The mother was a hedge fund manager and her son, William, went to the local prep school. Katie got William dressed and off to school and spent the rest of the day doing chores and seeing friends before picking him up from school, giving him tea and putting him to bed. In the holidays they would fly to the US together to spend time in the family home on Long Island while William's parents worked.

Katie was paid in cash and had no contract - until a month ago. After not being paid for a fortnight, she confronted her employer, to be told that the family had hit hard times, they were moving to a cheaper rental home and that she would have to go. Shocked, and still owed a fortnight's wages, she fled home to Australia.

According to Kate Baker, the director of Abbeville Nannies in Clapham, the “bonus belt” of southwest London, Katie's story is not unique. Nannies on her books earn £500 per week after tax, equivalent to a salary of more than £35,000 a year. “Nannies are losing their jobs because employers are losing theirs and the bonuses are being swallowed up,” she says. “The good native English-speakers are still highly sought-after, but those from central Europe or the Philippines are more likely to be affected.”

Of the 116,000 nannies in Britain, 76,000 are living in London, with just 18,000 working in the South East, 4,500 in the South West, and 17,500 in the Midlands and the North. In Starbucks on Northcote Road, Clapham, the heart of “Nappy Valley”, nannies have gathered for morning coffee. Janey, 27, who lives in a flat close by, says she could pay her rent with savings for a few months without work. But for Alex, 25, a live-in nanny to four children whose parents are both bankers, the prospect is more worrying. “I'd be homeless with nowhere to live if I were made redundant,” she says. “I'd probably have to find a relief job. A month's notice to find a home and a job isn't long.”

Both would be prepared to be more flexible and do a nanny-share if necessary, but agree that the salad days of the so-called supernanny, who could command her price and demand a flat and car as perks of the job, are on the wane.

However, it is not just the supernanny who is threatened. Alice, 30, a part-time nanny for three days a week to two girls aged 2 and 4, says that the credit crunch has already claimed her as a victim. “It was a big, big shock. I'd felt something was in the air for a couple of weeks and then one evening the mother told me that they could no longer afford me. She was really upset,” she says. “They have parents close by so they will be taking over my role and the youngest will go into nursery a couple of mornings a week, which will be much cheaper.”

Speaking on her last day at work as she watched two-year-old Emilia play in the leisure centre, she fought back the tears. The children had been told only the day before that she was leaving and both were upset. “It's very hard because I've become a part of their lives and they have become part of mine,” she says. “I'm more their aunty than their nanny, so I'm dreading this evening. The oldest one was very teary this morning.”

While it is her first time in 11 years as a nanny that an employer has said that they cannot afford her, Alice believes that there is still a demand for good nannies in London and has decided to set up her own agency.

Tinies is among the largest childcare providers in Britain. Oliver Black, its director, expects to see more luxury supernannies, who work for stay-at-home mothers, lose their jobs in coming months, but his company has also recorded a surge in nanny-sharing, as a result of the credit crunch.

Last year Tinies had 500 nanny-shares on its books. By July this year it had more than 1,000. It is, says Black, the perfect answer for parents wanting to cut back on costs without compromising on their childcare. Nanny-shares cost half as much as a sole-charge nanny but the same as a nursery and offer more individual care.

On Northcote Road, Janey is philosophical. Bad times are coming, she believes, but if parents work and employ a nanny it is probably the last thing they will let go. “We are vital for them because we're the people who organise their children and their diaries. They're much more likely to get rid of the second house in the country first.”

Some names have been changed

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