The father of Ashya King has revealed he was convinced to seek help for the five-year-old in the Czech Republic after an NHS radiologist told him proton beam therapy was "superior" to conventional treatment.

Brett King and his wife Naghmeh sparked an ­international police hunt when they removed their son from Southampton General Hospital on August 28 without medical consent and took him to Prague to receive proton therapy on brain cancer.

Mr King, 51, has previously spoken out about a threat by doctors to take Ashya into care if they refused to accept conventional radiotherapy, a claim the hospital has denied, and he has now revealed it was a consultation with an NHS radiologist that convinced him they had to leave.

"I said: 'If you had a ­five-year-old boy who had a Grade 4 (the most aggressive grade) brain tumour and you loved that son, what would you choose, proton or normal radiotherapy?" Mr King said.

"He scratched his head. I could see 1,000 things going through his mind. He said, 'It's not that easy'. I told him he'd answered my question. He then told me that it was all about funding and that the proton panel would never approve it. Then he said, 'If you're asking me about quality of life, proton is superior. With radiotherapy, your son will get secondary tumours'."