5 December 2012 Last updated at 17:37 ET

Hunt for missing brain tumour boy Neon Roberts

Sally Roberts, also known as Sally Leese, was last seen with her son in Tiverton

A search has begun for a mother who is believed to have run away with her seven-year-old son to prevent him receiving cancer treatment.

Sally Roberts, 37, also known as Sally Leese, was last seen with Neon Luca Roberts on Sunday in Tiverton, Devon.

The boy is at the centre of a High Court battle about whether he should have radiotherapy for a brain tumour.

Devon and Cornwall Police said the pair may have been in the Sussex or Kent area.

'Huge concern'

Neon recently underwent surgery for a brain tumour and doctors treating him said he was in need of urgent medical attention.

Police said it was believed his New Zealand-born mother was opposed to further treatment and may have disappeared with him as a result.

Mrs Roberts is involved in a court case with an NHS trust and council officials over whether Neon should have radiotherapy treatment.

A High Court judge made the decision to name Neon on Wednesday, despite him being at the centre of ongoing legal proceedings.

Assistant Chief Constable Chris Boarland, of Devon and Cornwall Police which is coordinating the search, said there was "huge concern" for his welfare.

He said the pair were believed to have been sighted in the area of Sussex or Kent on Wednesday, but their current whereabouts were unknown.

About 30 officers are involved in the case.