Research found 24million admit not brushing at least once daily.
As a result nearly a quarter quizzed are ashamed of their teeth — and 41 per cent say they feel too self-conscious to smile for a photograph.
A third said they notice the discoloured teeth of others.
The study of 2,000 adults found the worst brushers are those aged 26 to 34, with half not cleaning every day.
The most careful are over-55s, 68 per cent of whom brush at least once a day.
The worst areas are London, Northern Ireland and Wales while the best are the North East, South East and East Anglia.
Dr George Sotiropoulous, of whitening toothpaste maker White Glo, said: “We were shocked to find so many Brits not taking their oral hygiene seriously. Brushing at least twice a day is important to keep teeth and gums healthy.
“Even if you only brush your teeth once a day, it should be at night to ensure food debris is removed from the day.”
Speaking on similar findings in 2013, Chief Executive of the British Dental Health foundation, Dr Nigel Carter OBE, told the Daily Mail: “What surprises me the most is that some of these things are basic hygiene tasks.
“It is troubling to learn that people still have a poor attitude when it comes to their oral health.
“Anyone who regularly skips brushing their teeth morning or night is storing up oral health problems for the future such as tooth decay and gum disease – the biggest cause of tooth loss.
“Brushing last thing at night removes the deposits which have built up from eating and drinking during the day, as well as removing plaque – the cause of both tooth decay and gum disease.
“The last brush of the day also coats the teeth with fluoride, which is not washed away through eating and drinking, and continues to protect the tooth’s surface further during sleep.
“Flossing is also something that really is not a luxury.
“Removing food stuck in between your teeth close to gum lines is a really important step to preventing gum disease, and the most effective way of doing this is to use interdental brushes or floss.
“Brushing alone only cleans 60 per cent of the tooth’s surface, so this is an excellent way of keeping plaque at bay.”
-The Sun UK