Mobile phone firms are set to flood Oxfordshire with communication masts in a bid to improve their service, even though previous plans have provoked strong opposition.

BT Cellnet and Vodafone want more masts - some of which do not need full planning permission - to plug gaps in their networks. They have denied that masts pose a health risk.

Orange is also searching for new sites but would not say whether any locations had been earmarked in the county.

James Stevenson, community relations manager for BT Cellnet, said: "With 11m customers, we have got to maintain our quality of service and extend our network coverage.

"The whole of Oxfordshire is badly served by the existing network, so we are looking to fill the gap."

Jane Frapwell, an electro-magnetic field advisor for Vodafone, said the firm needed to upgrade its network to allow visual images to be displayed on mobile phones.

She confirmed the Vodafone was looking to adapt existing masts but had been in talks with Oxford City Council about its need for more masts in the city.

Applications from phone firms going through the system include a 15-metre lattice tower in Medley Manor Farm PYO, Binsey Lane, Oxford, and a 15-metre mast at Oxford Business Centre, Osney Lane.

There are also plans to erect a mast at Shipton Road, Woodstock.

Proposals to install masts have been greeted with fierce opposition in the past and mobile phone companies have been accused of failing to seek residents' opinions.

Fears have also been raised that emissions from the masts are a health threat.

Parents of pupils at St Swithun's Primary School, Kennington, Oxford campaigned to have a Vodafone mast outside the site removed despite being told it was safe.

Schools were originally offered several thousand pounds to have masts placed on their sites but Oxfordshire County Council banned them within 200m of schools in October 1999.

Oxford City Council rejected BT Cellnet's mast plans in Marston Road, between St Michael's First School and Milham Ford School.

The council's planning officers objected to the application because the phone company failed to consult either school about its scheme. The firm is to appeal.

Sue Mortimer, head of St Michael's, said: "I am disappointed that BT Cellnet feel they need to appeal because I agree wholeheartedly with the city council's decision.

"But we would be pleased to be involved in any consultation because we were not consulted in any way initially."

New Marston South Residents' Association branded the proposed mast insensitive.

A spokesman for Oxford City Council's planning department said: "National planning law allows certain types of telecommunications development without the need for full planning permission.

"For masts below 15 metres, full planning permission is not required, but details of the siting and appearance of the mast must be submitted for approval."