Imagine: there you are sitting at your shiny desk on day one of your new life as a Master of the Universe when, at the end of the office, you see your boss marching purposefully towards you with your CV in his hand. "You lied!" he booms, in front of all your new colleagues. "Get your things and get out." And it's only 9.30am.

This is a scene that really happened - to a lawyer, no less - and it is one that is likely to be played out with increasing frequency as more and more of us take to lying in order to seek advancement in the face of ever tougher competition.

According to The Risk Advisory Group (Trag), a consultancy which carries out pre-employment screening for some of the UK's biggest companies, more than 50% of all CVs contain lies of some sort, with one in five featuring whoppers such as falsified exam results and work experience.

Trag checked out CVs submitted by 3,700 applicants in 2005 and discovered discrepancies ranging from omissions about bankruptcy and county court judgments, through to downright lies about exam grades and employment histories. Researchers even found one applicant who fabricated a degree and four years' attendance at a prestigious university, when in fact he had attended the university's poor relation - and failed his exams.

"We are finding more and more instances of people lying, presumably as competition for jobs increases," says Sal Remtulla, head of employee screening at Trag. "Sometimes you have to chuckle at their audacity in believing that no one will check them out, but it is our job to ensure they don't slip through."

Our disingenuous lawyer - she will only be called Melanie - would almost have slipped through the net, were it not for her greed.

"I had exaggerated one A-level grade a little but everything else on my CV was absolutely genuine," she says. "I was three years post-qualified, so this was my chance to earn some decent money. On my CV I wrote details of my current position and salary, and at the last minute I decided to bump it up by £500 so as to get a good head start. Well, I got the job and the rise I was hoping for, plus the £500 I'd already tagged on. What I didn't realise was that details of my salary would follow from my last employer. My new firm was small and my senior partner was fairly hands on - he saw the details from my old firm, then pulled out my CV and I was rumbled.

"He said that if he couldn't trust me with the firm's money, how could he trust me with clients'? And, of course, he was right. I had never been so embarrassed in all my life. And all because I lied on my CV."

And if you cannot trust a lawyer, who can you trust? Well, no one, it seems. CVs accompanying 25% of job applications in the financial services sector apparently contain serious discrepancies.

One applicant claimed that he had worked for three months in Japan before resigning. Further inquiries revealed that he had, in fact, been arrested and deported for shoplifting and assaulting a shop assistant.

Other applicants had lied about criminal convictions and their dates of employment. Dates might seem trivial - mistakes are easily made - but on CVs they can take on huge significance. "If you've been fired by one employer, then stretching the dates of your previous employment and your subsequent job could help you cover up the bad period in the middle," says Remtulla. "But checks will catch you out."

And if you lie, you might find yourself having to cover up another blank spell in your employment record, to account for a period spent as a guest of Her Majesty.

"Generally speaking, lying on your CV isn't a criminal offence," says Raymond Jeffers, chairman of the Employment Lawyers Association. "But once you begin obtaining money under false pretences because you have lied on your CV, then that is deception and fraud. It is a very unwise thing to do."

So why do so many of us do it? According to Dr Colin Gill, a psychologist who has conducted research into lying and the workplace, many of us want to "impression manage" potential employers' view of us or "self-deceive" to make us feel better about ourselves.

"In a competitive world, you might want to make the most of what you have done," he says. "So let's say you played rugby for the university rugby team and you once answered a letter. Then on your CV you describe yourself as the former rugby club secretary; that would be impression-managing. It usually involves overegging and being economical with the truth.

"The self-deceivers are a little more troubling, because they go round making false claims that they actually believe. Those who simply lie - people sometimes described as pathological liars in the popular press - actually suffer from pseudologia phantastica, which is a habitual compulsion to tell lies. This is the sort of behaviour demonstrated by Jeffrey Archer when he lied on his CV. It is very often the case that everyone knows about the lie but lets it go until the person appears to be nearing a position of power - such as when Archer stood for London mayor. Until then, a lie on a CV doesn't matter that much. Grades can be falsified by impression-managers and self-deceivers. The difference is a self-deceiver believes he deserved that grade. When it becomes dangerous is when a self-deceiver actually believes he can fly a plane and sits down at the controls to fly it."

And whether you are an impression-manager or a self-deceiver, just because you got away with it at interview and got the job, do not think that you are safe. A retrospective check can still find you out.

Earlier this year that is exactly what happened to David Edmondson, chief executive of Radio Shack, the third-largest electronics retailer in America. Edmondson, who was rumoured to be on a seven-figure salary, had lied when he joined the company 12 years ago about a bachelor of science degree that he falsely claimed to have earned at the Pacific Coast Baptist Bible College in California.

After being caught out, and with a due sense of understatement, Edmondson said: "I clearly misstated my academic record and the responsibility for these misstatements is mine alone." He was then kicked out of one of the biggest jobs in corporate America. Following his dismissal - and with the collapse of Enron still at the centre of big-business thinking - many US businesses are checking out the CVs of all their staff. And history has demonstrated that what happens in America today happens here tomorrow.

So you might be OK for now, but odds are that the dirty little secrets on your CV will come back to haunt you. And in these days of easy-access electronic information, it is not so much a question of if as when that happens.