Residents in north Oxford were horrified to discover that a mobile phone base station was being erected on top of a roof overlooking their homes.

Notices posted around Oakthorpe Road, off Banbury Road in Summertown, warned people that the road would be closed on Sunday morning for a crane-lifting operation.

People living near the BT telephone exchange on the corner of Oakthorpe Road and Stratfield Road later found the crane was being used to erect equipment for transmitting and receiving mobile phone signals.

Kasia Benda, of Oakthorpe Road, said: "I think they have gone behind our backs. "We were given practically no warning that this was going to be put on top of the building.

"After the crane arrived at 8am on Sunday, we found out that they were going to erect a base for mobile phone equipment and our jaws literally dropped when we saw it. The building is already quite ugly, but now on top of this we are going to have this monstrous installation."

The work has been carried out by Crown Castle, an independent company that has a contract with BT to provide mobile phones services at its exchanges to improve existing fixed line facilities.

An Oxford City Council spokesman said the local authority had been advised that three antennas, two dishes and two pieces of receiving equipment were going to be put on the roof of the BT telephone exchange.

He said: "The letter was sent as a matter of courtesy because the proposed development is permitted under the Town and Country Planning Act, so the city council has no power over it.

"We have been contacted by a number of people about the work, so we will be sending a planning officer along to make sure that it falls within the confines of permitted development."

A Crown Castle spokesman said the development did not need planning approval but the firm had told the council about its plans as a matter of courtesy. Kate Williams, of Oakthorpe Road, said she could not understand why the company had the power to install the equipment without consulting local people.

She said: "Another mobile phone company wanted to put a mast on the Prama building in South Parade, Summertown, but it was eventually turned down by the city council on the grounds that it was in the middle of a residential area, near schools.

"Just a couple of hundred yards the same thing seems to be happening, but residents have not been informed about it at all."

Another Oakthorpe Road resident, Amelia Turner, said she found it hard to accept that she had had to go through an extensive consultation process to obtain planning permission for a single-storey extension, when the phone company had been able to put up the equipment without even telling people living nearby.

She said the metal work was completely out of keeping with the surrounding residential area.

Mrs Turner, who has a 10-month-old baby, said: "We are also really concerned about the health implications of this equipment because we are the ones who have to live and sleep by it."

Anyone concerned about the development should call Crown Castle's community relations team on 0845 601 4815.