When Denise Zaccaria's children grew up and left home, she felt it was time "to do something for myself".

So, at the age of 42, she decided on breast implants. "I was still quite young, and wanted to have a nice figure again. I thought of it as a treat, like a facial or pedicure. It didn't occur to me that it could go wrong."

The Nottinghamshire office manager tried to be responsible in choosing a surgeon, asking friends for recommendations. She finally found what she thought was a reputable clinic, and paid a visit.

"As soon as I walked in, they tried to book me in for surgery. Then they kept calling me. I felt pressured and didn't trust them," she says.

Then a friend suggested a clinic she'd heard about in Manchester. "I made an appointment and met a surgeon, who was from abroad.

"I had one brief meeting and he was keen for me to go ahead quickly. He seemed nice and I decided to trust him. I was never warned about complications, just that my implants would probably last 15 years."

However, a few years after the operation, Denise felt a hard ridge under her left breast.

"I thought I had breast cancer and was petrified. Soon, both breasts were hard and tender. I could no longer sleep on my front and my breasts started to look unnatural."

Denise was suffering from encapsulation - where scar tissue adheres to the implant. It's a complication in up to one in ten breast operations. But no one had warned Denise.

Her experience is not unusual. Experts warn that many women are having cosmetic surgery with no idea of the risks.

Inspired by celebrities and TV makeover shows, more of us are turning to surgery to improve our looks.

The number of procedures has risen from 202,000 to 700,000 in just four years. And with Christmas around the corner, clinics are experiencing a boom.

"We've seen a huge demand for vouchers, and we expect to see even more in the run-up to Christmas," says a spokeswoman for Transform Cosmetic Surgery Group, Britain's largest chain.

According to the British Association of Aesthetic Plastic Surgeons (Baaps), many people choose treatments such as Botox injections at this time of the year as a treat.

To cash in on this booming market, some other clinics are breaking the law.

A recent report from consumer watchdog Which? exposed an array of hardsell tactics, including offering patients discounts to book immediately (against the industry's code of conduct), advertising Botox (illegal) and using "before and after" photographs without making it clear the results are not achievable for everyone.

Which? says all this breaches the letter and spirit of codes of conduct of the regulatory bodies that govern the industry's behaviour.

None of this comes as a surprise to leading cosmetic surgeon Dai Davies. He is a former research fellow and examiner for trainee surgeons for the Royal College of Surgeons, as well as a consultant in plastic and reconstructive surgery at three London NHS hospitals.

He has long been concerned by the lack of industry regulation.

"It's been going on for years," he says. "The Government had the opportunity to do something about these abuses, but chose not to by opting for self-regulation.

"Cosmetic surgery is big business, so it's not surprising to get the 'pile 'em high, sell 'em cheap' mentality.

"Many women spend more time picking a bathroom suite than choosing their surgeon. Yet surgery is a serious matter."

Davies says patients don't realise the true complication rate of their chosen procedures, or may be at risk from "cut-and-run" foreign surgeons who fly to Britain to perform conveyor belt operations, then disappear home.

"I would urge women to be careful of foreign surgeons who fly in from abroad. They may meet the patient only on the day of the surgery.

"Also, British training is longer than in Europe. You can get on the specialist register in Greece after three years. Here, it is six."

Consultant plastic surgeon Norman Waterhouse, a former president of Baaps, agrees.

"The principles of best practice would seem compromised as the surgeon would operate, then leave the next day, which doesn't allow for continuity of care," he says.

Face-lifts, tummy tucks and liposuction also have high complication rates, including nerve damage, chronic pain and even death.

Former Scotland football captain Colin Hendry's wife, Denise, nearly died in a bungled liposuction operation five years ago, when her bowel was pierced six times.

Last October, she was rushed into hospital suffering from a recurrence of the blood infection that put her in a coma for five weeks and left her badly scarred.

In a separate case, surgeon Brian Gwynn, 54, is facing an inquiry by the General Medical Council after being accused of leaving at least six patients disfigured and in pain after breast operations.

The Medical Defence Union, the biggest provider of medical indemnity to doctors, has paid out just under £8.5 million in compensation and legal costs over the past ten years to patients harmed by cosmetic surgery.

"Some patients have unrealistic expectations of what can be achieved by cosmetic procedures, and what risks are involved," says Dr Christine Tomkins, deputy chief executive of the MDU.

Dai Davies urges caution. "Most cosmetic surgery is safe, because it is performed on healthy people, but bad cosmetic surgery is with you for life."

When Denise Zaccaria was told by her GP that she was suffering from a complication of her surgery, she chose not to return to the clinic where she'd had the operation.

"Instead, I chose a fully qualified British-based surgeon at a Reform clinic. This time there was no hard sell. My surgeon was very honest.

"He warned me that encapsulation could happen again, and that the operation would involve the removal of scar tissue, making it more complex.

"He wanted two consultations with me before I went ahead and, because of my fear of cancer, insisted on a mammogram and ultrasound scan between the two.

"The results of my second surgery are great, though it hurt more afterwards, probably because of the scar tissue removal."

Here, Dai Davies explains the health risks of the most popular forms of surgery:

• BREAST AUGMENTATION: Small risk of internal bleeding and infection. Much higher risk of encapsulation, where scar tissue builds up around the implant, causing pain and a strange look to the breast.

• LIPOSUCTION: The third most popular cosmetic surgery procedure, with demand up 90 per cent since 2005. Complications, while rare, can be serious. Internal organs can be punctured, leading to blood poisoning, and clots that go to the lung. Patients can go into shock, develop infection or suffer injury to internal organs. They can also be left with dents, lumps and sagging skin.

• TUMMY TUCK: There are many complications involved, and some surgeons think of it as a two-stage procedure. The first to do the operation and the second for "touch-ups", such as removing excess skin. There can also be problems with wound healing, scarring and infection.

• FACE-LIFT: Immediate risks include bleeding, scarring, asymmetry and lumpiness. Nerve damage is common. All patients will have temporary numbness, but for one in 1,000 cases it is permanent. One in 100 can be left with an asymmetric smile.

• RHINOPLASTY (NOSE JOB): While complications are unusual, this has a high dissatisfaction rate. Some patients can't breathe through their new nose or are unhappy that too much was taken away.

• EYELID SURGERY: Sometimes too much skin is removed from the lower eyelid, resulting in "scleral show" where the lid is pulled down too much so you can see the white under the eye.