The police officer who led the successful search for a severely-ill boy, who had been removed from a hospital in England to Spain by his parents, has defended the handling of the investigation.

Three days ago, an arrest warrant was issued for the parents of five-year-old Ashya King after they had failed to return him to a Southampton hospital.

Last night, the couple were arrested near Malaga in southern Spain, where British police have reportedly arrived to question them.

The family said they had taken Ashya to Spain against the advice of doctors in Britain because he was not getting the treatment they wanted after having a brain tumour removed.

The boy's father, Brett King, described the search that was mounted as 'a ridiculous chase'.

Assistant Chief Constable of Hampshire Police Chris Shead said he was aware the police's approach had created a "significant amount of debate".

"We had medical experts telling us that Ashya was in grave danger. Medical experts were saying to us that if he didn't get the care that he needed, there was a potential threat to his life," he said.

"Faced with those circumstances, I make no apology for the police being as proactive as we possibly can to actually find Ashya and ensure that he gets the help he needed," he added.

Ashya has now been taken to a local children's hospital in Malaga where staff are liaising with doctors at Southampton General Hospital over how to care for the boy. 

The case has demonstrated the desperate lengths some will go to in order to treat the seriously ill.

Ashya's father said the family was hoping to get to the Czech Republic, having been dismayed by attempts to treat his son in the UK.

His parents had been seeking proton beam radiotherapy - currently only available to treat eye conditions on the NHS in the UK.

Countries throughout Europe are, however, already using proton beam for a range of cancers in adults and children.

According to Cancer Research UK, the treatment differs from X-ray methods by aiming proton beams at cancers.

It works by sending charges into cancer cells, with doses of radiation aimed directly at the tumour. At the same time, the treatment spares healthy tissue, particularly tissues and organs behind the tumour.

The treatment is popular because it has a lower risk of side effects, though others are concerned that the long-term impact of the nascent procedure is not yet known.

In a video blog posted on YouTube prior to his arrest in Spain, Mr King said he was prepared to raise the money to pay for his son's treatment in Europe.

"Proton beam is so much better for children with brain cancer," he said. "It zones in on the area, whereby normal radiation passes right through his head and comes out the other side and destroys everything in his head.

"We pleaded with them (in Southampton) for proton beam treatment. They looked at me straight in the face and said with his cancer - which is called medulloblastoma - it would have no benefit whatsoever.

"I went straight back to my room and looked it up and the American sites and French sites and Switzerland sites where they have proton beam said the opposite, it would be very beneficial for him.

"Then I spoke to them again, I wrote a letter which he never responded to, saying OK - I will sell my property in order to pay for the proton beam."