London - The invite drops on the doormat in an envelope that looks delightfully expensive.

You rip it open and are delighted to be invited to a swanky black-tie do. There is only one problem - you have already made plans with the girls that evening.

Without a flash of conscience, you immediately make a lengthy excuse to your friends about your husband working late and finding it impossible to get a babysitter, before rushing upstairs to find your cocktail dress.

Congratulations: you are a fully paid-up member of the Social Gazumpers Club. You are a Socialiar - someone who fibs in order to get out of pre-made plans.

It seems that two thirds of those who break plans admit to lying in order to cover their tracks, according to Lastminute.com’s Living Life at the Last Minute report. Chartered psychologist Dr Lynne Jordan believes our increasingly packed diaries - from social engagements to work meetings and children’s swimming lessons - may be partly to blame for the phenomenon.

The ease with which we cancel is also down to modern technology. It’s so much easier to lie via email, text, or social networking sites.

“It is easier to lie because your friend will not see the non-verbal clues you are giving out, such as making over-exaggerated eye contact,” says Dr Jordan. “Plus, you don’t have to see the disappointment on people’s faces.”

Pity, then, the woman - whom we shall call Debbie - who cancelled a dinner to celebrate her best friend Kate’s husband’s 40th birthday because, quite frankly, he was a bore.

She quickly rustled up a “sick child” before heading out for a night with her girlfriends - and walked straight into the restaurant where Kate’s husband was having his celebration. “I don’t think Kate has ever really forgiven me,” says Debbie, 38. “She has never invited me to a birthday party again.”

Sick children are often wheeled out by gazumpers as an excuse. One friend of mine has even earned the nickname “Lastminute.vom” she has used it so much.

Dr Simon Moore, principal psychologist at London Metropolitan University, says: “People use a concept called social diffusion when weighing up whether to attend a party or not. Put simply, we tend to think that if lots of people are invited it won’t matter so much if we don’t turn up, because it”s less likely we are to be missed,” he says.

“And the more empathy we have with others, the less likely we are to gazump.”

The ultimate gazump has got to be the dropped date. Holly, 30, from West London, admits: “I remember once cancelling a date with someone I’d met at the gym to go out clubbing with friends instead. I texted him saying I sick, and should really stay at home. Later, I got one back saying: ‘I can see you on the other side of the dance floor.’

“Awkward doesn’t quite cover it.” - Daily Mail