Mid Sussex residents have vowed to fight an application to extend a mobile phone mast close to their homes and a school.

The mast, owned by Mercury on Little Park Farm in Hurstpierpoint, is 15m high but mobile phone operator Orange wants to share and extend it to 21m.

Residents of nearby Trinity Road fear the taller mast will be a blot on the landscape.

Alan Burns, who lives with his wife Dorothy about 20m from the mast, said: "They won't put masts on schools any more, yet there is St Lawrence School 250m away, a health centre 135m away and a play area 60m away."

When the mast was installed in 1999 it did not need planning permission as it was only 15m high.

Since then, Mid Sussex District Council has changed its policy and all operators need permission for masts.

Charmayne Diamond, who owns a Grade II listed house opposite the mast, said she was disgusted a phone operator was able to erect the mast without any planning process.

She said: "I didn't buy my house to have to look out on that thing. How can they just do this? "

Alison Uttley, a dentist who lives about 30m from the mast with her husband and four young children, said: "We feel incredibly let down by the planning department.

"Even though the health issues can't really be taken into account, we don't know how the mechanism works and if it is having an effect.

"I would not send my children to a school with a mast on it, yet 24 hours a day they have this beaming down on them."

The residents hope to object to the mast at a planning meeting, likely to be on September 9.

A spokeswoman for Orange said: "More than 60 per cent of Orange sites are on shared or existing structures. To accommodate Orange's proposed telecommunications equipment, the height of the existing site would need to be increased to 21m."

The city council recently rejected plans for five masts on health and environmental grounds, against the advice of their own officers.