The research, by healthcare analysts Laing & Buisson, also found that more than a quarter of UK dental patients now pay privately for their care.

This includes a growing number who are enrolled in private dental benefit plans.

Higher private fees have driven up income levels at the same time as only marginal increases in NHS fees Philip Blackburn

Laing & Buisson put the increase in private income - now at azn average 51% - down to private prices growing at a faster rate than NHS prices.

Private fees are now approaching double the fees dentists receive from the NHS.

In addition, treatment options available to private patients - particularly cosmetic and specialist dental treatment - have continued to increase.

Researcher Philip Blackburn said: "Since our last survey in 1998 the proportion of patients paying privately 'on the spot' for dental care has remained relatively unchanged though the number of patients enrolled in private dental benefit plans has grown strongly.

"However, income from treating private patients has grown strongly from 38% to 51% of total income as higher private fees have driven up income levels at the same time as only marginal increases in NHS fees. "

Dentists' response

The British Dental Association said the growth of private dentistry was being driven by rising patient expectations.

Dentists want to give their patients the best care they can Dr John Renshaw

Dr John Renshaw, chair of the BDA's Executive Board said: "The value of the private dental market has increased - though we doubt as rapidly as this latest report suggests.

"Our research shows that 65% of dentists still get more than 75% of their income from the NHS and this has remained stable over recent years.

"Most family dentists provide both NHS and private care.

"Dentists want to give their patients the best care they can and patient expectations are rising with people wanting more time with their dentist and a wider range of treatments, like white fillings, that are not available on the NHS."

Dr Renshaw said it would be misleading to argue that the increase in the value of the private market was simply because of a rise in fees.

Other factors were involved, such as the fact that more private work was being carried out and more expensive treatments were becoming available, such as implants and whitening.

BDA research suggests the value of the private dentistry market has grown from �289m in 1994/5 to �1.027bn in 2000/01.

Dr Renshaw said :"Our research shows much of this growth is in treatments that are not generally available on the NHS, for example white fillings, bonded crowns, and increasingly, implants and whitening.

"The BDA wants to see a thriving private dental market existing alongside high quality funded NHS provision which is available to all who want it.

"Action must be taken to address the under-investment in NHS dentistry over the past ten years and the workforce crisis facing the profession."

Billions generated

General dentistry in the UK generated an estimated income of �3.7bn in 2001/2002.

Patients spent a total of �2.5bn on general dental care, with approaching �1.9bn spent privately and �0.6bn spent on NHS charges.

Despite government policy to make NHS general dental care more accessible to adults and children, the number of adults registered for NHS treatment, though now stable, is still 1.5 million lower than in 1998 and 5 million lower than its peak in 1993/94.

Around 75% of people who buy private dentistry pay for it 'on the spot' out of their own pockets.

The remaining 25% pay through some form of annual funding scheme. The proportion of patients covered by dental benefit plans has grown strongly from 20% back in 1998.

Government defence

A Department of Health spokesperson said there are now more NHS dentists than there were five years ago.

"Over 90% of people can get access to NHS dentistry when they need it, by phoning NHS Direct - about 10,000 people do so every month.

"Two million more adults were treated in 2001/02 than in 1996/97, an increase of 8%.

"We have invested nearly �150m in the last two years to support and modernise NHS dentistry."

The spokesperson said further reforms of dentistry were in the pipeline.