Scientists say the system, which involves pressing one key per letter before the phone works out what word the user wants to type, trains young people to be fast but inaccurate.

They claim this makes them prone to impulsive and thoughtless behaviour in everyday life.

Modern mobile phones come with a built-in dictionary which enables them to predict what word a user wants from only a few key presses.

Each key represents three letters. It differs from an older system in which users had to hit keys several times per letter, for example pressing the 5 key three times for the letter L.

But it can lead to embarrassing miscommunications because some words use the same keys. For example, it is easy to end up asking a friend out for a quick riot (pint) or telling them about being stuck in a Steve (queue).

The study compared the mobile phone use of children aged between 11 and 14 with the results of IQ-style tests they took on computers.

A quarter of the children made more than 15 calls a week and a quarter wrote more than 20 text messages a week.

Professor Michael Abramson, an epidemiologist who carried out the research, said: 'The children who used their phones a lot were faster on some of the tests but were less accurate.

' We suspect that using mobile phones a lot, particularly tools like predictive text, is behind this.

'Their brains are still developing so if there are effects then potentially they could impact down the line, especially given that the exposure is now almost universal.

'The use of mobile phones is changing the way children learn and pushing them to become more impulsive in the way they behave.'

He added that the effects could have dangerous repercussions for a whole generation.

Experts concerned about the possible impact of mobile phone radiation on developing brains say that parents should be wary of allowing their children to use mobile phones too much.

But the researchers said the amount of radiation transmitted when texting is a mere 0.03 per cent of that transmitted during voice calls, suggesting radiation is not to blame for the brain effects.

Instead, Professor Abramson, from Monash University, Melbourne, believes functions such as predictive texting pose more of a risk for those whose brains are still developing.

'We don't think mobile phones are frying their brains,' he said. 'If you're used to operating in that environment and entering a couple of letters and getting the word you want, you expect everything to be like that.'

The study, which is published in the journal Bioelectromagnetics, will now be extended to look at the impact of mobile phone use on primary school children.

Previous research has shown that predictive texting makes people sloppy when it comes to spelling, with many flummoxed by words such as questionnaire, accommodate and definitely.

But it is so popular that some of the mistakes that regularly crop up due to words sharing the same keys have been turned into a slang language by teenagers.

They can be heard describing something as 'book' when they mean it is ' cool', for example.

If a mobile phone predicts the wrong word, the user can scroll through a list of alternatives.

In 2007, a total of 57 billion text messages were sent in the UK, with 6 billion of these sent in December alone.