Mobile phones can improve your memory ... but only if you're a man, according to latest research.

Tests at Bradford University showed that men who held a mobile to their ear during trials had better powers of short-term recall than men without them.

The results stunned the researchers in charge as they expected the phones would have had no impact at all.

But they say their tests prove that phones do, in a small way, affect the brain.

However, these claims were denied today by the Mobile Phone Association.

The new results published in Neuro Report specialist research journal revealed that men using mobile phones made fewer mistakes than the ones without phones. Women were unaffected.

As a result the scientists were today backing Government advice to use them with caution.

Dr Jim Smythe, senior lecturer from the University's School of Pharmacy, said: "I thought there would be a negative effect. I thought the phones would not interfere with the brain's ability to process information so it was backward to what I was expecting.

"The fact that mobile phone exposure influences brain function in any way could possibly mean that cumulative exposure might well result in damage.

"For the mobile phone companies this must be disappointing that there was neurological activity at all."

Thirty three men and 29 women aged 18 to 53 took part in the memory tests.

They were asked to stare at a pyramid with words in it, then after a break they were given a blank piece of paper to redraw the pyramid with the words in the right places.

Some of the students held mobile phones to their left ear while they were memorising the pyramid. In all, exposure to the phones lasted 15 minutes.

Some phones were on, some were off but all were silent. But overall the men with working mobile phones did better than those with non-working phones.

Dr Smythe, who works on the effects of drugs on animals' brains, added: "I don't think it is a big impact, I am not convinced it is that powerful, but there was an impact."

Dr Smythe uses a handheld set himself but advises caution especially among teenagers.

He said there was no explanation why women were not affected.

It could be the tests weren't hard enough for the female brain, he said.

"Females are more able to process information from one side of the brain to the other than men.

"The men remembered better rather than the women doing worse. They paid better attention after exposure to a mobile phone.

"There are some anatomical differences. Overall a man's brain is slightly larger but the female brain interacts better between each side than the male brain."

However a spokesman for the mobile phone operators' association said recent tests had shown no effects on the brain.

"Recent studies in Europe have shown no effect on human brain function caused by mobile phones.

"Independent scientific review bodies in the UK and around the world (including the World Health Organisation) have consistently concluded that the weight of scientific evidence to date suggests that exposure to radio waves from mobile phones operating within the international exposure guidelines do not cause health problems.

"However, they have also concluded that there are gaps in scientific knowledge which require further research."