It has become the benchmark for a generous salary. So why do its recipients complain that earning £100,000 a year is an expensive business?

In those idle daydreams about the perfect job, that fantasy promotion, it is a wage that - for the overwhelming majority of us - will do very nicely indeed.

An annual income of £100,000 is enough to put a recipient comfortably within the top 2% of all earners, and the figure has become a key indicator that the recipient is a high-flier.

The BBC's Panorama survey of the best-remunerated public servants took £100,000 as its yardstick - and it found that some 38,045 state employees take home that amount or more each year. Going by official figures, that leaves about 545,000 privately employed people earning £100,000 or more per year.

It is a sum that puts one within touching distance of the prime minister's earning power - David Cameron having taken a 5% pay cut upon assuming office, bringing his salary to £142,500.

It's like a gilded cage Geraint Anderson, Former banker

But what is it actually like to earn such an amount - generous beyond the imagination of most Britons, more than sufficient to guarantee a comfortable lifestyle, yet scarcely enough on which to fund an early retirement?

One of those who knows, and found the experience wanting, is Geraint Anderson, 38, who was earning a base salary of £120,000 and a bonus of £500,000 by the time he left investment banking after 12 years in the City.

Anderson, who documented how he became disillusioned with his lifestyle in an anonymous newspaper column and his book Cityboy: Beer and Loathing in the Square Mile, indulged in many of the cliches for which the sector has become notorious.

But he says earning such figures skews one's expectations of what is a normal lifestyle, and ultimately robs high earners of the freedom they believe money will bring.

Analysis David Kuo, of investment advice website Motley Fool The average person in the UK spends around £32,000 a year. This is made up of £25,000 on basic expenses (transport, food, clothing etc) and £7,000 on mortgage repayments. The upshot is that the average household needs a gross salary of about £45,000 just to break even. That is why, I reckon that the average person won't be happy unless they earn around £50,000 a year. However, it is may still be a hand-to-mouth existence. A salary of £100,000 a year can make a huge difference. After tax, this works out at £65,310. And after average expenses, there should be around £33,310 a year left over. Someone earning a salary of this size could retire in reasonable comfort provided they invest their disposable income carefully. They could amass a pension pot of around £550,000 after 10 years and almost £1.8m after 20 years. Of course, this assumes that a person on £100,000 is prepared to live modestly, spend carefully and save diligently. Top public pay: the numbers

"It's like a gilded cage," he says.

"They earn huge amounts but they have the massive mortgage, they have the high-maintenance trophy wife, they have the kids at Harrow - then they wake up on their 50th birthday and think, 'What a waste of a life.'

"They get into this culture where their worth is valued by how much they earn, so they work ridiculous hours. I'd rather earn £25,000, have the kids at a local school and not owe anyone anything."

Given that in 2009 median gross annual earnings for full-time employees was £21,320, few Britons will have much sympathy for those earning almost five times as much.

Yet while most of us can only imagine the bigger house, extra holidays and prudent savings that £100,000-a-year could allow, the reality of human nature is that earning more doesn't make us any more likely to live within our means.

Jasmine Birtles, personal finance expert and editor of moneymagpie.com, warns that, if anything, extra income is just as likely to leave us with less disposable income.

"The problem in this country is that we are very bad at budgeting because we don't plan ahead," she says.

"We have that whole suburban mentality of keeping up with the Joneses - moving into a new area, paying the big school fees but being six months behind with the mortgage. Earning £100,000 a year isn't going to change that."

There have to be incentives or people just wouldn't do this job Dr Peter Holden, GP

Indeed, the cost of living in some parts of the country means that the sum is barely enough to fund a loan to purchase a family home. According the Rightmove House Price Index for September 2010, the average home in London costs almost four times this high-rolling salary - £399,019. Of course, for dual-income families where one partner is on £100k the housing market starts to look less daunting.

Perhaps we should not be surprised, then, that a recent survey by the website lovemoney.com found that Britons who earned £50,000 a year were happiest.

But one top earner who will not be giving up his salary any time soon is Dr Peter Holden, 55, a general practitioner based in Matlock, Derbyshire.

Entitled to a salary of £106,000, Dr Holden - who was part of the British Medical Association team which negotiated GPs' remuneration package - insists he is worth every penny.

"I have a house worth £400,000, I drive a five-year-old Audi and my son goes to the local comprehensive school," he says. "My wife was complaining last night that we haven't gone out for nine months.

"I work a 60-to-62-hour week and I didn't earn a penny until I was 25. There have to be incentives or people just wouldn't do this job."

Whether he is right or not is for readers to decide. What remains uncontested is the old cliche about money not being able to buy happiness.