They were planned as eye-catching advertisements to safeguard the future of the country's 141,000 phone boxes.

The signs were placed on kiosks by BT as a money-making scheme because of increasing pressure from mobile phones.

But the adverts have provoked a row after unsuspecting shoppers complained of being hit by kiosk doors which phone box users can no longer see out of because of the signs.

Others have said they cannot see properly when making calls after dark because the ads shut out any light.

Now the Town Centre Business Forum in Brighton has written to BT demanding the adverts are removed or their design changed to make them more see-through.

The forum also complained the covered doors were a danger to women making calls late at night because they cannot see if anyone is approaching.

BT launched the money-making scheme last year.

Town centre manager Tony Mernagh said: "We have asked BT not to put adverts inside phone boxes. They are legally allowed to do so because of a loophole in the law, which says planning permission is not required to put adverts in the windows of buildings, and phone boxes are classed as buildings. I have seen two people getting clonked by phone box doors in North Street."

A BT spokesman insisted the adverts were made of a material designed to be see-through. He said: "The image is made of a material called confravision. It is made of small dots or stripes so you can see through to the other side. During the evening the image is reduced even more because of the light inside the kiosk.

"We are not aware of any incidents of people being hit by doors but we will certainly follow up what is said in the letter."